I am among those people who keeps getting back. Since Wotlk i have not fully played any expansion due to time constraints. However, i was getting 6 months subscriptions and i was hardly playing a month or 2. In BFA and in Legion i might i have played a little more but not in Shadowlands.
Basically, i am way more subbed than i have interest in playing, but i think this is now a lesson learned and i won't do a 6 month subscription again, not because it is a huge expense, which it is not, but because i don't want to pay anymore for something i hardly play.
I am not complaining any more, WoW is a game that i really love and i want it to thrive, i guess i outgrew the game and i am no longer the target audience but what i have now realized is that whenever the next expansion drops i will probably buy it but not accompanied with my usual 6month subscription.
Another thing is that WoW, nowadays, competes with so many different live service games, it is too hard for someone to retain more than one subscription whether is in the form of monthly fees or via season passes. Many good games are coming as well which will make the competition fiercer.