why is CSGO so hard?

CSGO is hard because you haven't learned the game.
Counter Strike as a series has 20 years of strategy developed.
CSGO has mechanics found in few other games, like economy.
Site takes are like a 5 player co-op speedrun. Everyone has to hit their pixel perfect smokes and flashes, if you don't you are doomed to die.

Study and you will improve.