Most young people that enlist in the military are not super patriots looking to become Captain America. They are seeking upward mobility, an escape from bad socio-economic conditions at home, or just looking for Uncle Sam to finance college after they leave the service.
Why are collegiate athletes any different? They are running in exchange for tuition money. Some are driven to bust their butts and some will just coast through four years of guaranteed financing. 99.8% will never sniff a pro career or an Olympic spot. What's the motivation beyond pride? You signed them. The rules state that you cannot cancel their scholarship unless they do something egregious.
It has always been this way. Either seek a new profession, dedicate your efforts to the kids that wish to improve, or start recruiting better (perhaps this is where you have become lazy?).