There doesn't even have to be a scammer involved. (Although is also clearly true that the entire ecosystem is a magnet for scammers)
Any of these schemes had to involve a much higher risk than conventional investing. You can wave your hands as much as you want, but that doesn't hide the fact that there was (and still is) systemic risk that was by a) nature incredibly difficult to quantify and b) probably pretty high, given the returns. There is no free lunch.
On the other hand, this was an epic level of fraud. As an example, I was making ~8-10% off of peer-to-peer lending when rates were very low, done via very (seemingly) reputable lending platforms. Imagining if a SBF-level scammer was running one of these, and I very much feel for those that put trust in an overall system that generally doesn't have this scale of fraud.