Item level’s pointless and as per many “high level players” even here on the forums, a terrible bar to use to judge a person’s skill anyways.
But they also don’t want to give up their precious item level gaps, because they want people to fawn over their gear, despite the gear being just numbers.
Casual people want to hit bigger numbers and clear content they enjoy faster to, but because they don’t play the same way as others it’s okay to demonize them for wanting more than absolutely nothing.
You mention you want higher level gear? Immediate responses is “Why do you want mythic level raid gear to do world quest!?”
Despite mythic raid gear never even being mentioned, people just assume. “What do you just want blizzard to mail you mythic gear?”
Or other stupid comments along those likes.
Casual players aren’t asking for Free Mythic Raiding gear, they aren’t asking for epics to be mailed to their inbox.
They just don’t want to do group content, because to be frank wow’s a toxic cesspool at this point I cannot blame anyone for not wanting to deal with other people, but still want to progress their characters. Otherwise why bother playing? That’s kinda where they are at. Stagnation, and everything being locked behind ridiculous group content filled with situations that are not enjoyable, and grinds that are not fun, will just lead to people leaving.
Casual players want content, and if wow won’t give it to them, they will just go play other games, which no one can pretend losing the casual player base is not a big deal to wow. 
We don’t care about your overbloated raids with a dozen things to keep track of per fight, we don’t care about your e-sports speed run garbage. We don’t care to engage in pvp (Which is arguably even more toxic than the last two). We just want to play a fantasy game and go pew pew at bad things and get rewards for it.
One day Blizzard will figure that out and actually figure out a meaningful way to keep casual players invested.
