Orcus on a bad hair day
Because the majority of the time, the rolls you make will be against foes. Count the rolls in any D&D session. Rolls in a single combat will vastly outnumber the number of rolls against static DCs.Why ever would you imagine that? If I am up against the mayor's cellar door it is somehow scaled number? No that isn't how it works
The things you are overcoming need to be more awesome too not just bigger numbers ... so why arent my skills allowed to do the same thing after all in combat I am taking down a swarm of Orcs (a squadron) at high level Or in humongous Dragon with attacks.