The spec says the description hash is used to commit to an associated description that is over 639 bytes.

things might accidentally work because the length is long enough.

(For me having the length decide on either storing a human readable string in a description or a hash for machines using the lengths of the string does not really makes sense - the app should explicitly choose. but that's how it is there.)

LDK, Phoenixd both don't support setting the description hash.

From what I heard LDK might support setting the description hash for long descriptions (as the spec says).

but that's also annoying for implementations (as discussed in the LNURL case) For plain LNURL the description hash requirement was dropped because of that.

This also means no human readable description can be passed along (that would be shown to the sender) (because it's either or)