Yes, single player games exist, but not all of them play the same way WoW does. Not all of them have the story, or characters that WoW does, someone who likes WoW’s story, but not the community, or not the dungeons is probably going to stick around for solo content and just stay out of dungeons, instead of finding a new game.
Also the vast majority of single player games have an ending. WoW does not, we get new expansion every few years. Some games get DLC sure, but most games only get 2 - 3 and WoW has 10 DLCs (called expansions, but they’re effectively DLC). This game is so large a new player coming into the game doing only questing could play for months and probably still have things they haven’t done. I started in shadowlands myself, and while I haven’t been exclusively questing, I still haven’t done anything from Classic, or most of the stuff from tbc wrath or cata. I haven’t even done anything on Pandaria outside of Jade Forest or raids and I’ve only quested through like half of Frostfire Ridge in WoD, so I still have tons of the “single player” part of WoW left to play, and I’ve been around for a few years now.
Can you blame them with all the “horror” stories players tell about dungeons? If I had never seen the inside of a dungeon and saw all the threads complaining about them I’d stay away too.
When I was a new player I got yelled at every time I messed something up (which was pretty frequently because this game does a bad job at explaining how to play). How was I supposed to know any better? I was new. One time I got yelled at in a dungeon just because I was a hunter lol.
It’s not always about the social part tho, some people just don’t have the skill to keep up, or find running through the dungeons at the speed of light to be stressful.
My dad tried to do Razageth twice, but he thought all the mechanics all at once was overwhelming and stressful, and it was hard for him to keep up with what was going on in the fight, so he stays out of raiding. He also mostly avoids dungeons unless I’m with him, because he played a healer from classic - wrath and got sick of dealing with randoms. He still likes the game, and he has fun playing, so he just plays it like a single player game that he can play with his kid when he wants to. Nothing wrong with that.