No, it’s more likely simply due to the fact that they don’t have enough loans to cover the interests on if let’s say someone deposits 500BTC. They keep the interest high on smaller amounts probably to increase the awareness, and because they can actually generate the amount of interest on these smaller amounts with their outstanding loans.

But it’s just stupid because i’d simply let a relative/lawyer open another account if i want to go over the 20BTC mark, right?

These lending services are just weird to me.