If you condense everything that can be condensed, the resulting style sheet could be harder to adapt to changing requirements.

One example of this is when some styles are "accidentally" the same for two elements. If you condense them into one rule, then you lose the independent control.

"Hey look, 97% of the users always turn up bass and treble together and turn down the middrange; we can condense the three-band equalizer panel down to one knob!"

This is why I personally like the Vue/React way of scoped CSS -- it promotes loading a simple baseline CSS (like Skeleton) for the full page and specializing in the individual component layer. It's easy to refactor in the case of changing requirements (if the same across components, move style into global CSS, if not, move into component).

Very nice to work with.