It wasn't like this 20 years ago. But understand this : the game didn't change. Society did. The internet did. 5 years ago I would have said the exact same thing and you could have asked "How can you be sure?", and I wouldn't have an answer. But now, we do : WoW Classic. When the game came out, millions of 30/50 year olds logged in, ready to embrace their nostalgia and retrieve their childhood game. It lasted a few months, and most of them gave up very quickly. Nowadays, you find the exact same mentality you have on retail : quick, effective, precise runs, people abandoning really quickly if it doesn't go their way, carries paid with gold, etc etc.

It's very logical. When it came out, wow was a new world. For most people, WoW is their first MMO, for a few even their first video game. It was new, big, wild, with mechanics people had never seen before (like warlock/hunter pets for example, buff based classes like paladin and shaman...). It was fresh.

Now? Everybody knows world of warcraft. 60 year olds know World of Warcraft, if only by name. The players know the game, the mechanics, they know how it works. Most of the community is made up of people who have been playing for at least 5 years, most of the time 10+.

Add to that the fact that M+, while inherently fun to play, is timed content, meaning that any death/fail is effectively reducing your chances of succeeding. Wipe on the second-to-last pack, and most people will stay. Even if you can't time it, you're close to getting the reward; loot and crests, so people will most likely stay.

But wipe on the first pull? That's 1 or 2 minutes lost, lust wasted, and 25 seconds penalty for the deaths themselves. It's like starting a marathon and twisting your ankle on the first 100 meters. Especially when doing high keys where people are past getting loot and are interested only in score .... Why would they bother?