Why do we want to learn so many openings......?

It's sort of like an arms race. If you don't learn openings while your opponent does then you're at a disadvantage in the opening.

Sorry, that sounded less dumb and obvious in my head.

I kind of understand OP as i share simillar view around openings. At least in my country, people feed even kids with opening theory way too soon and it's way too uninteresting gameplay in comparison to learning middle game and finals, which in my opinion are far more important as basic knowledge of chess.

The outcome of this, is that many people don't really learn how to "create" combinations and calculate advantages and gains, but rather memorize all opening moves until they no longer know exactly what to do but trying to force trades and little more.

Sure openings will be of major importance to a player rating but just when your facing masters and grandmasters levels that do really know opening theorys extensivelly.

I actually disagree with teaching openings to new players at all. Let them explore their own "responses" and develop their game by themselves, that's the real way to approach chess on any level, and not learning to memorize positions and variants.

Not everybody wants to learn so many openings.

There are many players who get creative from the very first moves and deviate from theory, partly because they are worried that their opponent might be better prepared, partly because they hope that their positional judgement will be better in unknown territory for both players.

Some such players have even reached super grandmaster level, look for example at some games of Baadur Jobava and almost all games of Richard Rapport, and (lesser known) greek grandmaster Ioannis Nikolaidis.

NITISH BAAPRA TOI CHESS TEACHER HOI GOLI RE

Because there are so many ways to go wrong, especially when a natural and seemingly principled move is weak.  You also save precious clock time by memorizing various lines and can recall situations where someone went wrong in a similar position (or avoiding it ourselves), but still asking ourselves "what is different?" because even a seemingly subtle detail can make their plan work (or not work). 

Openings are my favorite part of the game!