I think a lot of people feel that way, but it's more complicated than that. Some people struggle with writing simply because they're trying to write in a non-native language; in their own languages, they're fantastic writers.

But the other issue, even among native speakers, is that writing is a skill like any other — in the sense that you can be really weak in it while being really strong in other things. I've known some really brilliant researchers who are great at doing their work, and even great at explaining their work in person... but struggle tremendously with figuring out how to put it all down clearly on a page.

It's like other things in academia: some people are awesome at conceptualizing models, some people are awesome at analyzing data, some are awesome at figuring out how to present that data visually (e.g., tables, figures), some are fantastic at teaching, some are fantastic at writing. All of those skills are essential to the larger university enterprise, but it's unlikely that they all exist within any one person — and the good thing is that it's unnecessary, since research is often something of a team effort. :)