The rules of these games are made up anyway and winning is not an indication of any admirable real world trait or skill.
That exact same concept applies to card games, board games, betting, or any other type of interaction. Heck, most societies promote skills and traits that are not real-world admirable ("Oh look, that person can apply make-up so perfectly it appears they have no make-up on at all!").
My own answer to that question is likely to be less than satisfactory for you, sorry, but it essentially boils down to: Winning in a fair-ish game against stiff competition is satisfying, and makes me feel like I achieved something.
And sometimes they *are* real-world admirable traits... in competitive play, many games require high levels of dexterity, well researched strategies (including determining your enemy's tactics and countering them) and rapidly responding to tactical changes. Sometimes they also require deep levels of team-work, good coordination (and *fast* coordination as well). Games can also teach you how to react to stress, and time pressures (depending on the type of game you play, and how seriously you play it).
For example, League of Legends taught me about managing previously-uncohesive teams and forming team bonds quickly, as well as learning to recognise the difference between disenfranchised vs. deliberately anti-social players. This has contributed directly towards my ability to cope and manage real work situations where I need to help repair or manage ad-hoc interest groups amongst developers.
I guess all I'm saying is that you get out of gaming what you put into it. Gaming isn't for everyone, and surely some people waste their lives with games (and some games definitely do nothing other than waste your time)... but there is a lot you can gain from them as a whole.