Is it hard to cram 4 years of curriculum into 3? Or am I missing something here?
Depends on the program - the majority cut out 1 year of undergrad by requiring fewer courses in undergrad and/or require a few extra classes spread out over the three years and/or a summer session.
In general, students in these programs (by choice) take fewer advanced science courses than traditional pre-med students, and the reasonable GPA/MCAT requirements and guaranteed seat at medical school (don’t have to think about doing the “right” extra-curriculars, classes, etc in college to be competitive in med school) makes 7 year BA/MD programs MUCH less stressful than the traditional pre-med pathway.