why do people want to be good at chess?

Isnt it good enough to just be a weak player?  

the answer lies in the darkness of man.

ego.

( i could say  more but you are not of the cognoscente. )

it is a picture of my brother who sadly passed june 16 2011.  

Thanks, my brother is the reason i play chess.  He was stabbed during a game of chess when he took a pawn en passant and would not retract the move.  When he passed i made a point to carry on his passion for chess through myself.

In the beginning people may still be under the illusion that chess skill equals intelligence. So for example maybe they think they'd impress their friends if they were really good, or it would be an ego boost letting them think they're smarter than other people. Although I think it becomes apparent quickly that chess is not intelligence (it's practice like anything else).

So why do experienced players (who know it's just a narrow skill like anything else) want to get better? Sure for some it's ego, but at least to me chess games give you the impression that you could do better next time and at the same time it's hard to realize how bad you are heh. Maybe you overlook a hanging piece, or fall for an opening trap, and you know that with just a little effort, you could see noticeable results. Maybe next game you don't fall for the scholar's mate for example, and those small but noticeable improvements are motivation to keep improving... and of course no matter how good you get, you still notice flaws in your games.

The psychological aspect of en passant is discussed in good detail here.

https://www.chess.com/blog/VladimirHerceg91/using-en-passant-to-gain-a-mental-advantage