Not talking in behalf of Mark, but for me, not having access to some girls that I like, kept me away of playing. I'd loved to got Teru and Akizuki, also Bismarck and Prinz, but as far as I know, these are pretty rare or event-only characters.
At least in Girls Frontline, all the girls I like (9A-91, Suomi, G36, Wa and Springfield) are obtainable and I already have them in my team.
Some people cant just go to casual mode to some games or feel obligated to do the events because there is something that they desire in it. I did try KC casually and couldnt get into it as much as i like it, mostly blame my terrible luck as the major factor.
While I can only speak for myself, the problem with these sorts of games is that they make you feel like you have to be constantly working on them. They become part of your daily routine, and you just feel like spending however long it takes to do the dailies is as naturally a part of your schedule as brushing your teeth, no matter how much time they demand of you. I'll even set the timer on my phone to make sure I log back in at the right time and take bathroom breaks at work to whip my phone out and clear something if there's some time-sensitive event going on. It's not even fun anymore, it's just a compulsion where if it's not 100% clear, it's not enough.
Basically, it's not a matter of being "too hard", it's the fact that when you have that kind of personality, you can't just play half as much, there's only "quit cold turkey" and "continue devoting a significant chunk of your life to something you don't even enjoy anymore." (And Hell, I'm F2P in those sorts of games. If I was willing to spend money, I'd have really been on the precipice of ruining my life.)