Because I remember Stranger Things being a big deal for like a week back in July...
That's the problem with anecdotal evidence.
Also Game of Thrones grew in buzz every year whereas I don't think ST3 had nearly the same level of buzz as its first two seasons, at least from my perspective.
Stranger things has had more interest every season as well.
It's never going to have the buzz of a Game of Thrones, compare it to other high quality prestige dramas.
The trend data for that show is pretty low compared to the other shows you mentioned and various Netflix shows
I did.