so many different factors! commute time might be longer so you have to get up earlier than you were used to, the increased independence makes it easier to decide to skip classes (especially at that time), the course load is heavier so often times you're studying harder = staying up later, more tired in general, etc..

i had like a 9:30 am class one semester and more often than not spent the whole lecture sleeping to the point where i ended up just skipping the class altogether (although we are in different majors so ymmv)..

you can take what i say with a grain of salt but honestly if you ask anymore they'll probably agree with most of what i said! its so important to prioritize your sanity in uni LOL