There's an awful lot of middle ground between two to three serious and obvious fits and 15-20 "inquiries." You can expand or inflate the perceived interest as much as you'd like but it would still likely boil down to about a handful when it really comes down to it. It also depends in part on their ask. If they're just giving him away for the cap space then, sure, there would be a lot of interest but they're very likely going to want either quality futures or a really good roster player. I doubt 20 teams would make serious inquiries beyond kicking tires. Mostly, this isn't Hasek we're talking about here and it's not like they would be selling high either. Jose Theodore was traded for...David Aebischer. That's not the type of deal Washington would be after (a cap dump basically). Before that you've got to go back to Patrick Roy to find a Vezina winner traded in a legit hockey trade and there were very clear reasons as to why with the player wanting out. The precedent isn't really there league-wide, nor would I expect this front office to be the ones that blaze that trail.
The timing lends itself more to the possibility that Grubauer attracts a stronger market given a likely smaller ask (more along the lines of the Jones/Schneider returns), his stronger play this season, his youth and lower cap hit as a speculative #1 option for teams that are in between solutions.
You just materialized my main point. Holtby being on the market would be a precedent setting event. So I don't really see how you could sit there and tell us what that market would look like. (and I know we aren't comparing Holtby to Theodore...right?)