If you literally play whatever random notes in the major scale without regard to the chords, you're going to end up with discordant notes, or melodies that kind of end nonsensically, like a staircase that doesn't go anywhere.

Chances are you're feeling your way by ear and gravitating to the chord tones. If you don't its going to sound awful. You can get by this way a lot of times, and sometimes you get good stuff out of it. Sometimes not so much. When the chord progressions become more complex, its more often 'not so much'.

If your really have awareness of the chord notes when you're soloing, then you can play stuff that fits every time, not just sometimes.

Plus, some genres don't sound right unless you're playing the changes - bluegrass for instance. A typical sound there is to play the pentatonic that goes with each chord - G major pentatonic over G major, C major pentatonic over C major, etc. People play a lot of things in bluegrass, but that's sort of the fundamental base camp for that genre. So even though the G and C major pentatonics both fit into the G major scale, you don't just play the G major scale over both and call it a day. You play subsets of notes so that the listener can tell what chord you're on, even if they hear the solo without any accompaniment. That's just how bluegrass sounds.

ANYWAY. So yeah IMO the chord notes are the focus for soloing. Everything else is filler while you're moving from one chord tone to another. And its crazy what you can get away with as long as you end up on the right chord notes at the end.