If you know he is good at duping investors then you know he is good at gaining investors, and if you think you will be able to well time your exit you will make a shit ton of money off the other investor's investment. Many investors are just straight up gamblers and risk is just part of the game.

Its like people who invest into a ponzi scheme knowing full well it is a ponzi scheme, just thinking they are smart enough to leave before it all comes crashing down. And once you get enough critical mass, other people will invest based entirely on the fact that there is a lot of other investors and a rising price.