Fair enough on the criticism. Interesting Alta doesn't get the same criticism as Vail though when you have Snowbird closing way later than Alta when snowpack is good.
Vail has plenty to bitch about, but like I said, they sometimes get a lot of shade for stuff where others seem to get a free pass. Alta example I mentioned above being one of them. I rarely hear people busting on Alta for closing early.
EDIT: to @Uncle Louie point, there is a lot that goes into it. Not sure if I remember correctly, but I remember something about Alta's forest permit limiting them relative the Bird. But still......
Not sure how much of this is a factor for Alta, but there are clearly fewer skiers taking advantage of late season skiing, even though many of us appreciate how incredible good spring skiing is. Not only are there fewer skiers, but my guess is that the proportion of season pass holders to day ticketers goes up close to the end of the season as well. In short, the resorts aren't making as much money, which is one major reason why more resorts don't stay open later (USFS agreements and staffing are both legitimate as well).
If both Snowbird and Alta were open, they would be splitting the late season traffic, and it may not be profitable for either to stay open. On the other hand, if only Snowbird stays open, they consolidate most of the late season traffic into one place, and can (potentially) profitably stay open. Or even if they are operating at a loss at the very end of the season, being the resort that stays open the longest helps them sell more season passes next season.
We have a similar situation in the East where the few resorts that stay open past April, which may include Killington, Wildcat, Sugarloaf, and others, consolidate the late season traffic, allowing the resorts that are open to stay open. Eventually, everyone closes except for Killington. It's impressive how many people still enjoy Killington in May or even early June when just Superstar is open, but there just aren't enough people still skiing that other resorts could also try and stay open very late.