I struggled between Medicine and Ophtho as a medical student.
I actually matched in an Ophtho spot but decided not to do Ophtho, and turned down my spot -- hard to believe, I suppose, but if you think about it, how surprising is that? I thought about Ophtho purely because it offered a procedural field with a great lifestyle. But when I sat down to consider the clinical issues that I would be "seeing" every day and the fact that I would be "limiting" myself to the eye (lots of pathology there, don't get me wrong, just not involving other parts of the body), I honestly got a little scared. To me, the idea of not ever using a stethescope or never examining a patient's heart, lungs, or abdomen seemed, well, odd. I felt the field was limiting, though others would disagree with me. One person's opinion
I also have to admit that when Ophthalmologists tell you that their own field is overcrowded, that practice opportunities are limited, and that you should consider other fields, it has to make you think. 12+ years of school and training to not have some choice in practice location and not be in demand was not attractive to me. There are great Ophtho jobs around, but where are these jobs? Not in the major metros, or even 2nd or 3rd tier cities. Most opportunities for good paying jobs in Ophtho are in the boonies, unless you've got a parent or sibling already in practice. And if you get a job in the cities, many of these don't offer a partnership option, from what I understand.
When I told GI docs I rotated with as a med student that I was thinking about GI, they said "Great, come on in, we need more, and we'd love to have you". I NEVER heard the same sentiments from practicing Ophthalmologists I met or rotated with.
I did Medicine because I like the lessons about clinical care and patient management that you are imbued with in IM training. I really feel there is no better trained "Doctor" than a well trained internist. Biased, yes, but somewhat justified. In residency, we learn to stabilize and manage all sorts of patients with medical and surgical issues, and prioritize their care and treatment. I decided to do GI (thought Cards initially) and will start fellowship next year because I do enjoy procedures, find the subject matter and pathology diverse and multifaceted and involving more than just one organ system, still wanted to be an internist first, and quite honestly because it is a field in great demand.
I do think a lot of students going into IM name GI or Cards first in terms of interest because these are high visibilty fields with lots of clinical issues relevant to IM training and practice, and because they are fields in demand and that make $$$. However, I think it depends at which med school you are asking these questions. Med schools with strong IM residency programs that influence many of their students to go into IM tend to have a broader variety of answers to "why are you going into IM" including gen med, renal, heme-onc, endo, ID, etc. I know plenty of people in my own residency program (Parkland) that said GI or Cards during intern year but are now doing Pulmonary, ID, Endo, Heme-Onc, etc. People's tastes, interests, and passions change during residency.