In none of those cases did the market converge as a result of the insider betting, it was only discovered with hindsight that someone had placed a suspiciously

In none of those cases did the market converge as a result of the insider betting, it was only discovered with hindsight that someone had placed a suspiciously well-timed large bet. So that's where "they limit their bet amount for other reasons" comes in. I guess it's difficult to get a large loan for "I know a secret that will allow me to double my money in a few days, honest!" so they have to make do with their savings instead.