Some classes, when they reach a level that gives an ability score increase, don't usually gain any other class-specific benefits when they reach that level. (Examples: Barbarian, Fighter, Rogue.)
Others, particularly spellcasting classes, will get additional class features (such as extra spell slots or chi) alongside the ability score increase. (Examples: Cleric, Monk, Wizard.)
Why do some classes get extra stuff on top of what the other classes get? Is this balanced in some other way?
I thought that maybe it might have been balanced out by some classes having larger hit dice (so they gain more hit points when they level), but Cleric, Monk and Rogue all have a d8.