They're paid to start the project but not with the development. As you see, there are bunch of projects without any solid development and most likely, the owners of those projects just paid a developer and left them when it's already done. It is why it's very important to choose a project that has a solid development not just plan so your money is worth for each investment you'll do with those projects.
but sometimes even if they have comprehensive roadmap, still not an assurance that they can truly fulfill their objectives. imo, the most common reason why a lot failed is because of #1 item from the op's list. they really have no intentions to develop their project in the first place so they are focusing on how they can extract funds from those gullible buyers.
or in some cases, dev team has the passion but later on, once their funds dried out, they have no choice but to abandon the project. and investors are blind on that matter, as they can't see what's really going on within their developments