Why is Morrison's "JLA" generally considered to be the best Justice League run?

Is it because of the epic and wild scope of his stories?

Because all the characters are respected and they get their moments to shine. No character is portrayed as useless and unnecessary. They're all competent in their own way.

I need to read this.

I'm tempted to say the question is "what particularly good other runs of JLA are there?", though to be fair Waid's seemed pretty good from what I've glanced at and I actually really liked the tabletop League (the Amazo fight is my favorite in comics).

Though as for why Morrison's gets the most credit and probably is the best it's reasons already stated: he treated each of the members very well (except Huntress I guess), had really compelling and bombastic stories and came up with a lot of characters and concepts that stuck with DC for a long while (White Martians, 853rd century, Prometheus, Zaureal, etc.). Other runs I can think of don't have nearly as much impact.

I can't add anything that hasn't already been said, I would say the OP's query has been answered.

Great feats.

Morrison is a genius. He understands Hypertime and he didn't even create it.

Because Morrison is overexposed. His work is often what people read first when they get into comics, and being the first brings a sense of nostalgia.

Batgod

the angle back invasion was awesome. However the other story i like was the Obsidan league.

He really just fleshed out the characters.

https://comicvine.gamespot.com/articles/why-grant-morrisons-jla-run-was-the-best-team-book/1100-142643/