Why do Rogues get more ability increases than any other class apart from Fighters? As the mechanism of ability increases is an arbitrary boost, from the view point of class equality, why should a rogue get more increases than any other class except fighters? I can see why a fighter would get more as that gives access to feats, most of which are combat-related.
Rogues & Fighters in some form or another in previous editions of D&D gained more talents / feats as opposed to more spells or spell-like abilities. So it can be said that one part of this decision was to throw back to a previous version of the class.
Specifically at level 10 in 3.5 (maybe 3rd I do not recall) rogues had a small list of special feats they could access called Special Abilities.
A few of the 5e feats; such as Skulker, Dual Wielder, and particularly Skilled, seem to be directly lifted from that list as it was expanded over 3.5's long life.
The rogue seems designed for balance with this throwback feature in mind.