> - Becomes hard to make cross-cutting changes

This does seem like a negative, doesn't it?

But it's not. Making it hard to make cross-cutting changes is exactly the point of splitting up a repo.

It forces you to slow down, and—knowing that you can only rarely make cross-cutting changes—you have a strong incentive to move module boundaries to where they should be.

It puts pressure on you to really, actually separate concerns. Not just put "concerns" into a source file that can reach into any of a million other source files and twiddle the bits.

"Easy to make sweeping changes" really means "easy to limp along with a bad architecture."

I think that's one of the reasons why so much code rots: developers thinking it should be easy to make arbitrary changes.

No, it should be hard to make arbitrary changes. It should be easy to make changes with very few side effects, and hard to make changes that affect lots of other code. That's how you get modules that get smaller and smaller, and change less and less often, while still executing often. That's the opposite of code rot: code nirvana.