Really? What are they intended for? To reward academic achievement? Honestly, that's really more from organizations that don't tie an award to spending it at a particular institution, like United Way or National Merit. Merit scholarships from schools are another term for tuition discount, and are used solely to attract students with particular attributes (GPA, MCAT, geography, tuition discounts elsewhere, other desirable distinguishing characteristics, etc. ) away from peer institutions. Med school is no different from UG in this regard.
They are totally to pit schools against each other!!!! VERY few schools (HMS comes to mind) refuse to play, and those doing so are strong enough to not need it (like HMS), lack the funds, or are just okay losing attractive candidates to other schools, which happens every year. Very few people are wealthy enough to not have finances play a significant role in their decision. Schools are very well aware of this, and use money to pit themselves against other schools to be competitive for the applicants they want.
Even esteemed institutions like Penn and UCLA engage in the practice. If they didn't, NYU would be enrolling its pick of top students in the country that weren't eligible for significant need-based aid elsewhere, to an even greater extent that it is currently.
And yes, pretty much any doctor can pay off student loans. Period. But that's not the point. All things equal, I'd rather not have a $200-500,000 debt to service after med school if someone is willing to allow me to receive the education without it.