Why does everybody tryhard on seasonal event games?

I mean, I get why people copy decks that are strong in this meta, everyone wants to have a better rank, and using meta decks are the best way to climb said rank. But why do you do this on seasonal event games?
I stopped playing ranked games as much as I used to because one of the things I love about card games is the feeling you get when you craft a deck that actually works on your own ( which I mostly fail at ) . So I started playing seasonal because most people play with homebrew decks.

This season's event I thought that a NR witcher's deck would be amazing because you get twice the boosts on your deck, and you can flood the field with Blue Stripes and Dun Banners. Until I started playing against NG Assimilate/Spying decks. And I thought, thats an even better idea than mine (ofc), and suddenly everyone started playng the exact same deck. I mean 90% of my opponents use this deck and its gets really frustrating.

This is my first post and I just wanted to get this of my chest. Thanks to all of you that post something that actually helps improving the game.