EDIT: I'm speaking from the perspective of a local person. If you're applying from interstate, disregard things like distance from home.
Loads of reasons, some of which may be more valid than others.
- For many people, Adelaide (being in the centre of the city) is closer to them than Flinders. Flinders is quite far down south, and public transport isn't as convenient.
- "Direct" medicine versus provisional medicine: unlike UAdel, where you get clinical experience (sim patients etc.) from day one, you gotta wait till Year 3 (when the MD portion of your degree officially starts) to do that at Flinders. In first-year Flinders, you'll keep dancing around biology, chemistry and other "high school" subjects, which can get boring quite quickly, and things like anatomy will have to wait till later.
- Bigger cohort = more friends? There's only 30 students in your Flinders med cohort, versus 150+ at Adelaide.
- More of your friends go to Adelaide uni in general, so it makes sense for you to choose Adelaide med so that you want to be with them.
- Better campus life. I attended the Flinders o-week at the start of the year with my friends and it was pretty underwhelming ngl.
- This one is a very controversial reason but I think it's something that everyone has in the back of their head when applying for med schools: perceived prestige. I won't comment too much on this.
At the end of the day though, medicine is medicine, and everyone graduates with the same degree and qualifications.