Which ones are they?
First of all, I have NOT seen a liability EXCLUSION for trampolines. That’s why companies cancel you, if you get one. So I don’t think you can buy "coverage for trampolines".
Secondly, trampoline claims are actually a higher dollar payout, than dog bite claims, and thats why insurance companies don’t want to cover it.
I don’t know of any carriers who WILL write a homeowners policy if you own a trampoline.
But you can always lie on the application (not recommended), and when the trampoline claim comes in, you can pay it out of pocket – six or seven figures, if you’re talking about a child being paralized.