Have *you* read the manifesto lately? Because it literally says "Welcome changing requirements, even late in development."
Your comment actually exemplifies the biggest problem Agile as a movement has: whenever something about it is pointed at as causing a problem, even core principles of what Agile is supposed to be, the response from Agile partisans is always "if that's causing you problems, you're not doing Agile right". There is never any circumstance in which they will admit that Agile isn't the very best development method because their answer to any demonstrated problem with using Agile development (where their first go-to answer of "then do Agile harder" didn't work), is "well then you should stop doing that, doing things that don't work isn't Agile".
In other words "Agile means committing to doing things a certain way, except when that turns out not to work - then it means committing to not doing them that way." That's not methodology - of course Agile claims not to *be* a methodology, but a mindset! It's not even a mindset though, it's just constantly moving the goalposts so you never have to admit that sometimes what you advocate doesn't work all that well.
Look, I actually like the general ideas of what the manifesto is driving at - but at some point the movement has to realize that you have to *actually advocate something actionable*. If your answer to "but what you told us to do didn't work" is trite inanities like "Agile is a framework, not a methodology" and you can't say "not doing this is not Agile" about anything, then you're just saying "Agile is any time anything a team does works", and that's not an actionable mindset, framework or whatever you want to call it.
Commit! Put a stake in the ground, say "these practices are the Agile development methodology, *and if Agile doesn't work for you, that's OK*, don't do Agile then, it's not the only way to get things done".