idk if nesting is the reason people used tailwind. imo it's more that css itself is a lot of complexity and overhead to write if you already have nesting and reuse in whatever you're using to produce html, ex react. I'd rather not have to maintain a css tree and a component tree when it can all be colocated.
if you're copypasting you're not using the code reuse tools of your component library. the nesting in normal css is component nesting with tailwind. and if you're copypasting things that aren't just the same component styles but something else shared, it's just a string you can stick it in a variable.