I started learning scales almost from day 1 and I'm still learning them 30 years later.

Fact is that I've only learned what I think I'll most likely use which includes the diatonic major and all 7 modes, pentatonic major and minor, blues, whole tone, diminished, harmonic minor, melodic minor, chromatic and a couple others that I used more back in the metal/fusion days (hungarian minor, enigmatic and a others I've probably forgotten).
To me, the key to learning scales is in two parts:
1. learn the sound of the scale by it's intervals. A diatonic major scale sounds like a diatonic major scale no matter if you play it in A or A# or Db or C and this is because the interval structure of the scale remains the same. This recognition comes from constant repetition and practice.
2. learn when to use a scale according to what chord or chords are being played. This requires an understanding of chord progressions and how each chord is derived from the notes in a scale. If you know the chord and you know what scale the chord came from (according to it's root/tonic) then you'll know what scale(s) will work over that chord.
Basically, in order for you to know what scales (in the form of melodies, leads, licks, riffs, etc) to play over a song, you MUST understand the chord structure of the song. If you don't know the chords, you won't know what scales to play, so, learn the chords first. Then you can break down the progression and know when to play what over which. Sure, it sounds like a whole lot of thinking, BUT it's made much easier the more you do it and it will become natural after a while, trust me.