Sill a pretty small amount considering a majority of users are probably not going on-chain. I could be wrong, many exchanges don't support lightning and on-chain could just be the mechanism users use to "cash-out" (if they to purchase something using fiat)

netstatic

bitcoin

Are wallet companies sustainable?

Wallet Of Satoshi takes a .5 fee for base layer transactions and, in my humble opinion, provide an excellent service. Yes custodial is not the way for your savings but no one has made using lightning so seamless from my experience. Especially for no coiners who haven't used Bitcoin yet