Briel:
But when you start to see a half dozen games that the GM abandoned fairly early, that's a giant red flag to me.
This seems to me to be an over-critical assumption but, alas, is common thinking.
It takes two (and in RP, generally several) to tango. Just because a game is short, it has not necessarily failed, and even if it has, it is not necessarily the GM's fault.
There are many games that fail as a result of player attrition and sometimes, I might even say frequently, it doesn't matter how good the game concept is, or how enthusiastic the GM is, if the players don't want to play, the game is doomed.
This is particularly the case in less popular games where GMs struggle to find someone to give it a go, don't have the luxury of choosing the best six out of twenty applicants, and don't have an infinite supply of players to replace drop outs.
It also doesn't take account of GMs who experiment with different concepts, creating taster games and playtests that are
designed to have a short run, nor those who play strategy or board games that have a limited number of turns before completion.
Long games are often the result of a fortuitous synergy between the GM and the players.
The concept that 'Short Game = Bad GM' strikes me as a very myopic generalization.