While I do acknowledge that speedrunning is a thing and a challenge, on the other hand I don't really get why you would go out of your way to not play the game as much as possible.
I mostly level through dungeons at the moment, because I like group content (even if it sucks at the moment). Playing with other people seemed to be the raison d'etre for MMOs, but to each their own I guess.
Wouldn't it be great for those dungeons to actually be challenging, and to play with people you know and talk to through discord? Guess what, they are max level and don't want to level yet another alt. They also want you to be raid ready as soon as possible, so you can start raiding with them, but you don't want to play your highest level toon for this reason or that.
Then there are the people who have already leveled 2 - 5 toons every xpac, when it was live, and/or leveled numerous alts to catch up to current content. It is all the same old shit in the old content, which makes it something people have to endure, just so they can have fun with a new class at max level.
I like the fresh leveling experiences of a new xpac, the first few times, but there are many people who dislike the whole leveling thing, in its entirety. They just want to raid or do mythic+ with friends. Some hate leveling so much, they pay for a boost, others only want to spend $15 on this game, so they either endure the leveling boredom or, if it takes too long, end up quitting when their main no longer holds interest.
Speed leveling as some streaming competition seems silly to me (not that there is anything wrong with it), but shaving time off of a small part of the game that people don't find enjoyable shouldn't be hard to understand.