What does it mean to call a prose style hard?

And certainly law schools are not places known for their teaching of great English prose style.

A year or two ago, I fell in love - with a prose style.

She was critical of the author's tone but praised her prose style.

I read this over 15 years ago and found the prose style tedious.

One wishes too that she had demanded more of her prose style.

Of course, we do not elect Presidents for their prose style.

I asked him what he thought of Martin's controversial prose style.

All that glamour, and a prose style to die for.