A lot of it can be blamed on inexperienced / unskilled GMs. Its relatively easy to come up with a good RP concept. Its quite another to make it work long-term.
That's the main problem I've run into in the games I've joined so far. It is greatly frustrating because I expect the GM (and usually one or two co-GMs) to be the most committed to the game, but they've been usually the first to bail after introductory posts. It is easy to come up with an interesting RP concept players would join, but there's a huge amount of work after the second IC GM-post that doesn't seem to be considered.
Honestly, it's not good enough to excuse a sudden disappearance on real-life as a GM: 99.9% of their reasons were blamed on school work or something that they
would have known was coming up. Their contingency plans, namely their co-GMs, were incompetent, meaning they didn't take the reins as they should have until the GM returned or they ghosted away too. (I once had a game wherein the GM's internet access had been cut off, but the game had three co-GMs - THREE - and not one of them initiated anything to move the beginning plot along; in the sporadic times the GM could pop back, they didn't quickly authorise or prod their co-GMs to continue the game either).
That said, thanks for sharing your GM experience,
@Ellri. It might be a good idea to start a thread for GM tips: what they've come across, unforeseen flaws and what worked.