Listen, in general I agree with you, but it is a theory that was built only on observations without any theoretical foundation, and modifying the theory parameters every couple of years whenever a new observation was proving it wrong. I am sorry, but at this point MOND is on the same level with the flat earth theory and maybe it should be renamed as the conspiracy theory of gravity.

There are two problems with MOND. One is that it exchanges fine arbitrary parameters of dark matter with the arbitrary parameters of MOND. There isn’t a theory the explains MOND or the parameters. It is just as much of bodge as dark matter.

Second is that MOND doesn’t explain all the observations. There are galaxies that have too much or too little gravity. Either MOND varies exactly as we neeed it, or need MOND and dark matter. That isn’t any simpler. It might work if there was theory that explained smaller amount of dark matter and MOND could handle the rest.

The Bullet Cluster is typically touted as the biggest evidence that dark matter is right and MOND is wrong: https://en.wikipedia.org/wiki/Bullet_Cluster#Significance_to...

Basically, the center of mass in the cluster, and the center of the matter we can see, are way far apart from one another, in a way that ends up being super clear to observe. We can infer the center of mass by the surveying the gravitational lensing we observe, and we can observe the center of the baryonic matter by looking at the x-ray sources. The offset in distance here ends up being pretty clear evidence that most of the mass exists as stuff we can't see (in any wavelength, only via the lensing.)

This is a bit of an indirect answer, but I watched this not too long ago and it made it seem clear that MOND doesn't work so well, if not in general at least in the case discussed, which seems pretty damning regardless: https://youtu.be/HlNSvrYygRc?si=6on0pD9_jsed9Dlm

I've also heard the bullet cluster pointed out as a strong counterpoint to MOND--I'll let you read the wikipedia page rather than attempting to explain this, poorly: https://en.wikipedia.org/wiki/Bullet_Cluster

As a layman who watches tons of astronomy and physics videos, my general sense is that dark matter is more or less simply a placeholder, such that everything else around it is pretty consistent, but it just represents this unknown matter that we can clearly observe interacting _gravitationally_ with galaxies and other objects in the universe, but otherwise doesn't seem to interact. Whereas my impression of MOND is that it's a set of heuristics that requires a lot of tweaking to work, whereas GR is quite simple and very strongly experimentally verified. But, again, layman

This is a dense video, I highly recommend it though: https://www.youtube.com/watch?v=PbmJkMhmrVI

TLDW: there's a lot of evidence on why the phenomena we watch is mostly favored to be described as 'something' that is conveniently called dark matter as opposed to a revision of gravity.