lightning uses onions!

they don't make enough of that point nor do they really exploit it enough in their protocol design

part of the reason why payments fail is because they are client side onions and a hop in the path is ded or unresponsive temporarily 

 The massive centralizing routing hubs of LN reduce and sometimes even negate the benefit of onion routing. But this is besides the point because 95% of LN users are on custodial wallets or LSPs that give them none of that privacy anyway.