We don't do lip slurs for the sake of doing lip slurs. The object of doing physical rudiments should be to create positive results in our musicality. I will agree that physical rudiments are important and that we all need to do them. They isolate trouble spots in our playing by reducing the numbers of tasks to be done at once. Take long tones for example.
Long tones require only one task and that is to play a single note.
There's no need to spend mental energies on articulation, flexibility or anything else besides tone production. This is great when it's used as a rudiment. It helps us see things in our playing which we cannot see in a more active context. But the fact is, real music is not isolated to one physical aspect. Music requires a complex combination of all the physical elements.