The absence of quality goalies may be because many minor league programs in Canada were training small boys to be goalies. Often, the smallest kid was put in net. Technically, they might have been solid, but size stops a lot of pucks. In the mid to late 80's, the Jets had a number of goalies that were short and skinny. Alain Chevrier was 5'8" 180 lbs, Pokey Reddick was 5'8" 170, Lindsey Middlebrook 5'7" 170, Pierre Hamel 5'9" 170 and Daniel Berthiaume 5'9" 155. Bodies like this aren't made to handle 60+ games. With forwards and defense men getting bigger, faster and shooting harder, goalies with this frame were over matched. The bob and weave influence of the European game also challenged their lateral movement, which was not the forte of Canadian trained goalies at the time. Now, its difficult to find a goalie under 6'1" 200 lbs.
Yep, this is the truth.
The early 80s was also the apex of the more acrobatic form of standup style, partially due to the smaller size of the goalies: this was a time of flopping & diving, skating wayyy out to cut off the angle, skating into the corners & behind the net, & getting clobbered all the time. It was a style more prone to injury & it required more recharging time. The three goalie teams were usually two-goalie tandems with injury replacements sometimes ending up playing as many games as a backup does today. Nowadays the goalies are stapled to the spot in their nets & can pace themselves better over the season. Also, for the 82-83 season, the NHL expanded the roster size from 17 to 18 skaters, which helped create a seismic shift in the way the game was played, as teams could roll equal 4F 3D lines; Flyers revolutionized short shifts because they had the depth to roll 4-3 equal lines. A lot of players were phased out by that within a couple of years & replaced by players who could handle the new pacing, & the butterfly & playing deeper back into the net started to become a stronger strain in goaltending style, & goalies who didn't adjust got left behind.
Since the OP mentions Brodeur-Caprice-McLean, I'll explain the 3-goalie rotation for the Canucks through the Brodeur era. Brodeur, by the way, was 5'7" & epitomized the style I mentioned above. He was pudgy, especially after his injury in 83-84, & he had a tendency to skate out even further than most goalies to cut off the angle. He'd often get picked off by snipers on his glove side when he did that (Bossy & Potvin made mincemeat of him in the 82 Finals) & when Roger Neilson's crease-clearing army disappeared, he was exposed as a goalie who always flopped, he could be drawn down on the blocker side & get killed on rebounds & garbage goals. When he bulked up & lost his speed he was toast as a starter, but after the 82 run the Canucks re-signed him to a big, fat long-term contract that came back to haunt them later on when no team in the league wanted to touch Brodeur.
In 79-80, rookie Glen Hanlon won the starting job for the Canucks & was touted as the goalie of the future for the team, with an .883 over 57 games his first season. But he separated his shoulder & kept reinjuring it through the 80-81 season, so Brodeur emerged as the starter. The Canucks had picked him up in the offseason from the Isles - he was third string behind Billy Smith & Chico Resch & spent the year in the AHL after being a veteran starter in the WHA for several years. He was 28 when he joined the Canucks. Gary Bromley replaced Hanlon to backup Brodeur while Hanlon was out.
In 81-82, Brodeur was playing much better than Hanlon, so the Canucks basically gave up on him at this point & shipped him off to St. Louis & got 5'10" 165-lb Rick Heinz in return as part of a package, who never really showed much of anything while in a Canucks uniform.
82-83 Canucks dealt for veteran John Garrett to back up Brodeur, because he was being backed up by career minor leaguer Ken Ellacott. Garrett impressed immediately because he replaced the injured Brodeur in the All-Star Game & won a three-star selection. In the meantime, Canucks junior prospect Caprice impressed as the backup helping backstop Canada to a gold medal (winning his only 3 starts) at the World Juniors that year.
83-84, Brodeur went down to injury, but Caprice badly outplayed Garrett that year & won the starter's job late in the season while Brodeur was down: in 19 games, he went 3.39 & .882, compared to Garrett's .851 & 4.10 in 29. Brodeur returned in time for the playoffs, relegating Caprice to the press box.
84-85 - big drama year: Brodeur showed up to training camp overweight, & new coach Bill LaForge - the worst, most disastrous, destructive coach in NHL history, bounced Brodeur to Fredericton, & I don't think he ever got over the humiliation, the already moody Brodeur became more bitter and cantankerous after this. The young & green Caprice was prematurely thrust into the starter position with the badly declining Garrett backing him up & a coach the entire team hated from the get-go. Poor Caprice was chewed up by teams like the Oilers that season, & after LaForge was canned Harry Neale kissed & made-up with Brodeur & let him take the barrage the rest of the season, the Canucks' worst. Caprice was never really the same after the LaForge experience: the flashes of talent he showed at the World Juniors & the 83-84 season never really returned.
85-86 & 86-87, Brodeur continued as starter with Caprice as backup, & new prospect Wendell Young pushed for Caprice's job. The aging, pudgy, moody Brodeur was among the worst starters in the league, but he was protected somewhat by defensive-minded coach Tom Watt.
87-88 regime change with Pat Quinn in charge, he finally remedied the disastrous goaltending situation in Vancouver by dealing Brodeur to the Whalers for Steve Weeks & by picking up Kirk McLean from the Devils, which essentially finally put Caprice out of a job. Captain Kirk with Weeks as a solid backup with Troy Gamble as the up and coming prospect was arguably the strongest group of goaltenders the Canucks had ever had in their history.
Canucks never intended for there to ever be anything but a starter + backup, but their ongoing goaltending woes usually meant a third guy was playing a lot, just like a lot of teams of that era.