Let down by parents - what do you think about this situation?

Typical asshole parents. My parents don't do that kind of thing to me because their parents did it to them their whole lives (both families being wealthy, like yours). I don't think they do it as if they were dangling a carrot, like you say. If you ask me, the problem is that they are so greedy and materialistic that it's just stronger than them. In the distance they will think reasonably. You are their son, it's a wise investment you'd be making, any way you want to see it, lending you the money is the right thing to do. But that's when the time to put up the money is far away. When that time comes, they just can't let it go, even if it's for a good cause, and even if it's a loan. They are not sadistic liars or anything like that, they are just greedy. The only problem is that they don't like to see themselves that way, so the temporarily lie to themselves by lying to you too.