probably a variety of reasons but heres a few.
The grind, you have to have A LOT of free time to get into an MMO and you don't spend 90% of that time having fun you spend it grinding for experience and gold.
High barrier to entry level, You can't just pick up an MMO and play it, no sir-EE! you have to study the mmo, breathe the mmo, you have to look up strategies for boss fights, character builds, and such online and if you don't do this people will call you names and while we all like to act tough and be like "I don't care if someone calls me a noob" in the end we really do, my proof is that A. We still call people noobs, and B. we feel the need to publicly announce how we are not upset showing we are clearly upset most of the time. MMOs and their players are harsh, you can't just join in a raid in WoW and enjoy it you have to have a certain item level, a certain sequence of spells, a certain balance of classes in your party or people will be mean to you.
Time/money: people who play mmos don't feel realistic because they but an abnormally large amount of time into it, by the time it takes you to reach level 85 in WoW you will have spent as much money on the game, its various expansions, and subscription fees as well as much time in real life as it would have taken you to learn how to play an instrument or learn another language. Quite frankly, when someone obsessives over something like a video game they are bound to come off as total weirdos and MMOs REQUIRE that you obsess over them to get any fun out of them.
I used to play WoW, and I would spend about two-three hours every other night on it, combined with 50$ for the initial game, 115$ on expansions and over 200$ on subscription fees.
I came out of that with bad eyesight, bad skin, and a short temper.
Now adays I do Karate twice a week for 4 hours, I made one initial payment of 10$ for membership and another payment of 40$ for the outfit, In the two months I've been doing it I went from tripping over my own feet and weighing 205 lbs to being able to easily perform 3 Katas, weighing 190 pounds, having decent skin, and a shit ton of patience. Also I can say each time I went to Karate I had a lot more fun than each time I played World of Warcraft and the friends I made in Karate are a lot closer than the friends I made online.
Despite this the classes I attend only have three students and are struggling to stay in existence where as World of Warcraft has millions of players and generates enough money to fix the United States economical issues.
Sooooo those are some reasons I think MMO players don't get as much respect as you think they deserve.