Yes there are stock music quality issues here, for general library standards. The main issue would appear to be the general quality of several of the samples used there, they sound distinctly dated and older compared to more recent sounds. This makes a difference to many customers, who very often don’t want more “vintage” sample sounds.
Also there are various aspects of the tracks’ arrangements that, while perhaps don’t break the rules of music theory, reduce the potential to support visual productions.
For example in the tropical track, the melodic development is continuous, incessant, with no breaks or rests for the theme breathe. This creates overstimulation and listening fatigue much sooner. Also the lead melody notes are always very fast and don’t stop or pause enough, to rest the theme, give the ear a break for variations, and then start perhaps again…
For good stock audio, this in itself is a significant production detriment, which hinders the ability of a track to better support the focus on the visuals of general video projects.
And that’s why the tracks would be rejected.
It’s also explained in the sections on Elaborate Solos and repetitions here