This is not a real issue, because the same thing can be said about C. No two C projects are the same, each has its own set of libraries, macros, types, etc.

I think the main problem is that Forth systems don't have a standard way of creating interfaces like C and other languages have. So the diversity of environments becomes a big issue because it's difficult to combine libraries from different sources.

I think it goes beyond that no, because you can do meta programming with Forth

That's not right. C coders have no problem at all diving right into most other C codebases.

I think like C, there's standard/ANS Forth.

But most likely lots of those Forth coders implement their own which don't necessarily conform to the standard.

Have you tried collaborating with Forth? There's a lot of documented history of people doing so in industry when it was actually used, and more recently I've usually found Forth codebases approachable and easy to follow.

Personally I think this is the pay-off for writing the code in the first place because Forth is very difficult to write in a clear way, if you actually manage to do it you've probably made it very clear to follow because otherwise it's hard to finish your project and make it work at all.

"Have you tried collaborating with Forth?"

No, I never did more than very simple experiments with Forth (which is why I started my comment with "what I heard").

"because Forth is very difficult to write in a clear way"

But that pretty much means, that the average programmer will have problems with collaborating.

Not for simple collaboration or modification, which is most of what you want to do. But yes any serious development is difficult in Forth, period.