I gave up after Season 7. To be fair I did have a social obligation watching with friends and pizza every week, and we spent Season 7 making fun of it before someone said "I think the show might be bad now" and we stopped.
Yeah I think I just watched to see how the Negan plotline played out and then I was done. It was starting to get stupid before then, but the Negan reveal where he killed someone and didn't show it in the season finale (tune in next season to find out who he killed!) was the point where I started to think "this show isn't getting better, it's getting worse."
It wasn't a conscious decision, just more of a meh, don't feel like watching it. It sent from a show I watched religiously every week to a show I couldn't be bothered with. The Negan plot-line could have been great but they went to gimicky with it.