Actually, Valheim is included in many pc website's/social media as a potential GOTY if not the GOTY but i see where your going at.
I dont feel valheim is a early access title only by name as its stable as rock, barely any bugs and offers 1000+h of content .
Did you play it? Would you put that on your top 5 favourite game you played last year(be in early access, beta etc etc or not?)
Its also not included in many too, for the same reason, that there are many who also have the same 1.0 rule. Different GOTYs have different rules, these are just mine and as I say nobody gets handed an award from my one, its just curiosity.
I did play Valheim, I put about 200 hours into it, maybe a bit more. I liked it, thought it was very good indeed. I dont feel like they really kicked on with it and added enough additional content but I'm sure that will come in 2022. I'd say yes if I was drawing up a list of my top 5 games played of 2021 Valheim would be in it, probably around 3rd or 4th on the list.