For real. The whole Patreon thing was a mistake. Developers have no motivation to actually finish their product because why would they ? They already have steady income they don't need to sell anything for profit. Infact finishing the game would mean they would have to come up with something else to keep people subscribed so finishing the game is not even in their best interests.
Also like you said they will make promises to people so they give them more money. Daily lives of my countryside is exemple of game that's overbloated with characters because the dev keeps adding more of them instead of finishing content for those already in the game.
I'll be fair and say patreon (or any monthly payment site) plays a part in the motivation
the thing that kills most devs motivation depends
1: Lots of Money (this is the leading cause of most big abandoned projects, once you get a livable income from doing basically nothing its hard for some devs to be motivated.
2: Over promising and being in way over their heads (This always leads to burnouts and a loss of motivation)
3: Loss of passion (another leading cause, if a dev keeps making a bunch of side games then it's likely their passion is waning)
4: Only making a game for money only (The main reason this site is filled with Koikastu/Honey Select/Daz Slop)
(There's obviously more reasons but i dont wanna make this too long lol)
From what I'm seeing is DC's reason for being so slow is poor management and having a shit tons of money
we still have fast devs like Majalis,Mity
and the kind of slow but consistent devs like Breadman