A personal note, I'm a native english speaker living abroad, with a non-native-english speaking superiors. While their writing is quite good, i find myself battling constantly for what we might consider 'better, more clear' writing, in favor of the current scientific writing 'trends' in our field.
A successful paper or two with a weird phrase or typo will end up reshaping that field to adopt this language, as authors of subsequent work attempt to align themselves to the original topic.
At least in fields I was familiar with, a lot of Ph.D. training focuses on making people into good writers. Clear communication with both peers and the general population is rewarded; it is damn near impossible to get ahead without these skills.
I don't know what you mean by "hard to read." A good scientific paper is supposed to be very information rich. It condenses 100 other very dense papers into 4 pages, leaving just a few pages for the new contribution of the current work.
Even for a very clear paper, for a field I am well versed in, a good paper takes 10 readings to understand. Because of the information density.
But synthesizing newly discovered knowledge that only a handful you know (and often don't even understand all aspects of), into something others can understand is far harder than you think it is.