According to the MSAR, something like 99% of the students at each school have bachelors degrees. I can only speculate on the 1% who don't.
Shall I speculate? That 1% has alternatively demonstrated the maturity and discipline to complete lots of very difficult academic coursework and to jump through administratively-specified hoops. They've done plenty to establish themselves as compelling candidates without finishing a degree. Or, they're compelling international candidates whose degrees don't translate here.
I also speculate that if you don't complete a bachelors, you'll get asked why, forever. When you interview for residency, when you interview for fellowship, when you interview for faculty, etc. If you want an MPH, JD, MBA or other addition to your MD, those programs are going to want a bachelors, I imagine.
If you don't want to do finish a degree, have a better reason than "didn't see the point." You can always apply without it and see what happens.
Best of luck to you.