At least What a Long is so shockingly easy, and has been in the game for nearly 20 years, that its barely even a concern for most people.

I was there when it was brand new, and short of a few hairy specific achievements in it, it was a throwaway background thing you did just to get people engaged with the holiday (that they would ignore otherwise because back then it was just flavor with little reward). No one really stressed on it, and anyone who cared about getting it was gonna play all year anyway. So they just had to spend a few hours in the weeks long holiday to be done with it, and get all the numerous other prizes (the meta title per holiday, the numerous other specific rewards you could buy every year from the holiday vendors).

A much worse version of what you are talking about is the Anniversary/Xmas rewards. Because those are not only just once a year, but they are only that year. If you aren't playing November-December 25th, you just don't get to have it. And it wasn't until like 2022 in that they started letting you get old Christmas gifts as rare drops from a holiday boss, and the Anniversary ones were only available again during the recent 25th event, and only some of them.