I tutor for sciences and at the moment a lot of my A level students have missed massive chunks of prior GCSE knowledge due to covid. Practicals we're removed from exams, etc, so the basics are missing in a lot of cases.
Others have come from schools where they only did combined science and are now in a cohort of peers who did three separate GCSEs, so again, missing content that the teacher may cover quite quickly if 95% have already done it.
Others have been excessively spoon-fed at GCSE and have found A-level a massive jump. Got a shock that they have gone from getting 8s to Ds. These need a confidence boost and guidance on how to become independent learners.
Still others just don't 'get it' the way they are taught it. The subject might have been something they were good at at GCSE, and they took the A level but maybe it's the wrong fit. They might not specifically need that subject to do their degree, but they do need ABB, or whatever, and it's too late to switch. So they get a tutor, scrape a B, and never use most of it again.
Also, students seem much more isolated that when I was at college, so some of them just want someone to bounce ideas off while they do their homework, just an hour a week of discussion using the vocabulary can make a big difference to a lot of them.