Well i feel the same. I would love to have the Ice Age, Ice King all year. It was fun to be honest missing it right now. Doing the casual legendary quest... feeling the game a bit empty.
I was never a fan of seasonal or any time gated or timed objectives, quests. When i was playing AOEO first time and met a time objective i quit the quest, then at when i first met with timed legendary quest i quit instant of that game.
I mean if an event is fun i would enjoy it all year non stop. If no fun then not.
It's a psychological effect, feeling like taking away a freedom factor. And turning the fun into a strict timed work like chore.
Also it's another psychological effect if a seasonal event was good experience... and it's gone for like a year... it creates a huge negative feeling until it returns.
Many leg quest has freedom of choice what i love, you can go with anything you want, you choose, inf, ranged, cav, siege, mass fortresses, priests, ranged ships harassment... whatever you like.
I feel if the winter event quests were available all year long then players would basically get bored of grinding them and it would make the "event" somewhat meaningless and reduce the drive to play them
So if the players are playing 6 quests all year instead of 12 quests... then they won't get bored of grinding that 6 ??? For like 9 years.
The Time Frame existence only drive people to play some map more often then others.
About burning out... you need to play it 24 hours 7 days... and have no work or being a full time dev, some of these type of guys can burn out after many years all who loved the game. But still there will be a good bunch of people who will never burnt out, if the game won't lose the things they love.
All the rest normal working people who got a few hours a day... won't burn out, probably they will be a bit confused to chose from 12 quests instead of 6.
So this argument is not valid. The only valid thing is people will play the event quest less often and mixing it up with other casual quests.
The seasonal dog bone is only a marketing trick, a tool for top managers to prove statistically for their employers or to the share holders that their genius project ideas are worth their multi-million dollar monthly or seasonal premium bonus.
On contrary for a casual player it's either has no any effect or produce a very bad effect and make they quit. Why? Because if it was a good event and they are missing it... they will search and find similar enjoyment experience in another product.
Variety has it's beauty and the best things project celeste do is to bring more variety to the game. Making an event seasonal is like taking away the fun when its offseason.
Rotating events each after each would be awesome to. Just don't have to wait months, that's killing boredom.