First off, I don't think quitting a game is - at all - a negative thing or some kind of slam against a game (or the weird 'failure' some people seem to view it as) a lot of the time. There are lots of perfectly fine games that aren't for me because of code or rules/setting, or that don't have activity at the times I can be around. I think most of the time people hang onto places they aren't enjoying for far too long. Nobody should feel bad for leaving a place they aren't enjoying or be guilted into sticking around something that's not for them.
There's a Star Trek game I tried numerous times and it's a good example of a place that just wasn't for me. I came up with some characters I liked and really enjoyed a lot of the STing in the plot scenes, but there wasn't the churn of 'social' scenes that I feel like I need to invest in a character/build relationships, and I was turned off by the amount of +job virtual paperwork necessary, even though I saw some benefits to it in terms of deciminating information.
I tend to drop off Lords and Ladies games because, while I like fantasy, I feel like they attract players who are really into a type of RP that I'm not (soft politics based around marriages and costume drama stuff).And if the majority of your fellow players are RPing stuff you aren't into, that's not gonna work for me. This is also why I tend to feel uninterested in very sandboxy games. If I can't engage with some sort of consistent game world, it gets just isn't the kind of world I want to play in.
I try lots of games I drop off of after a week or two because the character just doesn't grab me and my ability to invest in my PC is the thing that actually makes me want to play. That's on me. Motivation to do this stuff is more internal than I think a lot of players want to admit. I also don't think it's BAD. If there's nothing something I'm inspired to play at a given time, I'm happier playing video games or reading or whatever, and I'll circle back to MUing eventually when I have an idea I want to play.
I've also quit for what I consider actionable reasons based on staff abuses (oh, Steel and Stone) and just general Ugh-ness (oh, Battlestar Pegasus), but that doesn't fall under my 'quitting isn't bad' point and isn't what I wanted to talk about. Quitting is deserved and logical when staff is screwing with you or cheaters/harassers aren't being booted, but I honestly don't have a ton of negative experiences. Maybe because I tend to Out pretty quick when my annoyance level rises.