The copy and paste statement related to portability, and that's how I was defining it in this context. It was not intended to speak to Tailwind's maintainability.
However, a traditional class-based, modular approach to CSS can not guarantee portability in the same way. So if you can not predict what effect the same classes, or even the exact same HTML, will have, then it's neither portable nor is it very maintainable either.
> something you write in one place can be copy and pasted somewhere else
That sounds like the opposite of maintainable.