Software quality -- quality of anything -- is a function of how many intelligent, creative, experienced, capable people get involved. Such people are in extremely limited supply. Suppose that a number of such valuable individuals discover and become successful using AIJI technology (Acronym I Just Invented). Then, cargo cult thinking takes hold. The vastly greater number of less capable people see that these rockstar/ninja/wizards use AIJI. They think that if they start using AIJI then they too will produce great things.
Look, just because Jimi Hendrix and other guitar gods play Fender Strats, it doesn't mean that I will become deified just because I pick one up.
The superstars were going to succeed no matter what tools they used.
In the case of Agile: that isn't even technology, it's management. I'm sure we've all been under the thumbs of idiot managers who keep hearing the word "agile", believe that they should use this wondrous new thing, ("think" would be putting it too strongly and optimistically), pick up some vocabulary, and then do the same moronic things they've always done, but now calling it Agile. (Source: worked for a manager who had his daily "Agile" meetings -- I believe they're known as "scrums"? -- and they grew from 15 minutes to half an hour, to an hour to two hours, and that's not counting the time to get the shitty microphone working for the offsite people.)
Mediocre people will still find a way to be mediocre with Agile. They add features nobody needs - things like rounded corners, tagging, profile pictures, autofill, Facebook logins, more routing. Refactor two weeks a month. Or don't refactor at all - we're too busy working 60 hour weeks.
Agile tends to reward ticking off stuff. Sometimes the most important thing to do is improving a search, optimizing something from O(n^2) to O(n logn), or recommending the best thing to a user. But this is very vague, hard to measure success or improvement.
So it's easy to just add more bugs, more tests, more refactoring, more processes instead of doing stuff that matters.
The most mediocre people of all embrace this easy way out and focus their careers around the process of setting up meetings, documentation, and giant checklists.
It's when Agile is warped to fill a void of pretend work.
"You are saying we should listen to the customer? You are saying we should talk to each other and share ideas?"
If you think bootstrapping scrum is going to fix your inability to work as a team then you should probably cross your fingers too.