Here you can have help if you are dyselxic, or have some other learning difficulty, but the rest of it is up to you. The main reason, according to my uni's (UU and QUB) is that there is no way to tell what is a 'guidance' service and what is a thesis writing service.
And in truth, having completed both a BSc and a BA, and and MSc and currently on an MA, the differences in disciplines are vast. Grammar an structure is not such an issue in science subjects as it is in arts, where students are expected to have a grasp of language etc. So if you do a science subject, you are not judged on structure and the writing in teh same way you would if you were an arts student.
In short, if you are able to study to that level then you should not need to employ the services of anyone else. I can't speak for other universities, or even other departments as I'm aware tat sometimes departmental policy varies, but outside help is very frowned on here.
Look at it this way, if you are studying creative writing or english and need to pay someone else to edit your thesis, then you are probably studying the wrong subject.