It's just because they're arrogant and selfish. Nevertheless, when someone transforms into a greedy creature and then leaves the system, we can't predict, but it's really wrong to trust our gut at first. If you're confused why it's easy for people to get scammed that way, you'll need to see those people who have joined multi-level marketing or ponzi schemes. They are stupid enough to believe a stranger's word and fall a victim to the scams