If anything, it is the opposite - people will stay subbed longer if they can play alt jobs. It is week 9 right now, after playing my main role for 8 weeks I want to play other roles. But so many parties are locked to 615+ that I can't, so I'm just checking out instead.

Last tier, I kept playing but it was miserable, I had to play another 8 weeks before I had a weapon/chestpiece for one alt role I wanted to play, it was just really annoying how long it took, and even then I needed longer to get enough gear to have one tank/one healer/one DPS all fully geared. It wasn't fun, and by the time I had the BiS and could join BiS parties I didn't even wanna play anymore. That's why I told myself in the future to just give up on alt jobs and check out after week 8.