Many solists even some who are quite well known don ot improvise melodically.
They play patterns, or scales, or riffs but the notes they play never connect together to form memorable melodies.
Just playing a bunch of notes even if they are harmonically sophisticated and rhythmically complex doesn’t auto result in lasting musical statement.
Melodic imporvisation is the art of creating a continuous new melodic line using a son’gs existing chords — not just playing chord or scale based patterns.
Musicians who can create memorable melodic lines seemingly out of thin air are true improvisational geniuses. It is rare natural talent but one that can be developed. All it takes is a good ear, a decent melodic sense, and the ability to think beyond chords and scales and patterns to complete melodic lines.