personal issues (health, psychological, family etc)
don't get enough money (especially now with the mess the world is in)
don't have enough time
sure, there are also people that want to scam, don't care etc, but I don't think that there are as many you think they are.
life happens. There are companies that went bankrupt, and I'm talking about professionals, people with money, an established audience etc (ubi has to sold a lot to tencent if i remember correctly) that screw up. Sure it's sad, it's annoying, it's infuriating, but you have to make a choice: do i support x dev, knowing that i might get screwed, or i will not, knowing that that game may never see the light of day because I didn't support it. Well it's more complicated than that, but you get the idea