I think it's partly because the NHL doesn't directly compare to say the MLB or NFL (within the US, anyway), it can't just sit there and expect the general public to care.
Hockey, like Basketball is more of a niche sport. So it can't rely on a lot of "fairweather" fans to generate revenue - instead it relies on more dedicated fans of the sport. So many of the teams switch up their identities to generate more revenue.
Looking at the NBA, the following teams have drastically changed their look/colours during their tenure: Golden State, Utah, Houston, Dallas, Denver, Atlanta, Milwaukee, Toronto, Philadelphia, Cleveland, New Jersey & Washington. I'm ignoring tweaks to secondary colours/logos or switches in prominence of colours (San Antonio, New York, Orlando) and franchise relocations. That's 12 of 30.
Looking at the NHL, we have Vancouver, LA, Anaheim, Phoenix, Tampa Bay, Washington, Buffalo, Pittsburgh, Columbus, New Jersey, New York Islanders. I'll throw in the reborn Winnipeg (different franchise, but essentially the same identity for the purposes of this discussion), which gives us 11/30.
So the numbers are comparable. It's interesting that the "big"/"traditional" markets in both sports are generally absent from these lists - teams like New York Knicks, Boston Celtics, Toronto Maple Leafs, Calgary Flames, LA Lakers & Montreal Canadiens pretty much just have to be run reasonably well & continue to operate for the revenue to come in. It's the smaller or more marginal markets that are reinventing themselves to sell more shirts/jerseys/hats/bumper stickers.
Given the revenue the NFL & MLB have flowing in, it doesn't surprise me that there's less reinvention. A team like the Pirates makes money without having to work at it, purely because there's so much money in the sport (and a revenue sharing model that essentially guarantees them a cut no matter what they do on the field). Selling more merchandise is of course nice, but it's gravy for them as long as they get a cut of the Yankee's revenue streams.
Mayor Bee is correct about Hockey fans being fairly traditional - the more established & wealthier teams realise they'll make more money out of their established identities that they would out of the "travesty" of new designs. Let's be honest, I doubt that Leafs fans would buy a red & white jersey that's not some sort of commemorative (or 3rd) in great numbers. Instead they'd all whine about it.
On the other hand a team with far less tradition like the Ducks changed their logo, colours - the whole shebang - because they didn't have the same tradition, nor do they have the guaranteed sellouts the Leafs have. Sure, many fans think the Ducks colours/logo are awful, but they're not battling 50 odd years of tradition when trying to sell the new colours to fans. So they'd rather upset the apple cart a little knowing that their relatively limited fanbase will refresh their wardrobe from eggplant & teal to black & gold over time - generating more merchandising sales than would have otherwise been the case.