This question is pretty straightforward. I like rock music but I cannot figure out what scales they are using.
The majority of rock is played with the pentatonic scale. It is useful in many styles of music and just generally a good scale. The blues scale is just a derivative of the pentatonic scale; it, in essence, is the same except for the blues scale, which has one note added to it, the blue note, which is the diminished fifth.
The blues scale has often been used by rockers to add a blues flavour to their rock music; Randy Rhoads and Gary Moore and a slew of 80's rockers where quite fond of doing that.
The harmonic minor is heavily used in metal. You can, of course, use the melodic minor scale as well, but for rockers, it is a bit hard to play differently ascending than descending; rockers tend to be a slave to their patterns.
The Major just simply sounds kinda childish in metal. The major key in rock sounds like pop punk. Here is a video to illustrate what I mean.
As @YourUncleBob commented, the pentatonic and blues scales form the vast majority of rock music. This is not surprising as rock is descended from blues.
That said, more recently, rock and metal have been starting to embrace more complex scales and modes which is changing the landscape considerably.