If you are talking about the problem of "sending the last few sets" from a application, it seems ridiculous that no one has solved it, but actually, it is basically a massive security problem if you allow users to easily get down to zero Satoshi's, instead of getting down to say, one Satoshi or two Satoshi, or three Satoshi's in their wallet. The issue is that there are a whole class of attacks on the lighting network which involve extracting tiny fees from services and continually alternating between having a balance of zero, and having a small balance, say 10 Satoshi's. It's very tricky to protect against these attacks and at the same time easily allow a user to go all the way down to zero. It's no problem to let a user go down to like say three Satoshi's or five Satoshi's, but an easy zero for users is actually quite difficult to allow securely.