It's not a money issue at all. I think (naively I admit) that US coaches have an obligation to the sport to develop US runners. "The sport" is buttering your bread, allowing you to earn a living because someone, some where valued the sport of running. Chances are this "coach" was a scholarship runner himself, and has benefited. Now when it's his time to develop more runners, he starts hiring foreign talent.
Yeah, you can say the coach only has an obligation to win championships but does any AD give a rip? A guarantee they care even less if all the athletes are foreign.
I had foreign teammates in college. I even had a coach that was from another country. They were great guys. Was it "enriching" to have the around, Yes. BUT.. there were other runners that could have been in that spot.
If you want to watch more programs go down the toilet then yeah, field nothing but foreign talent. In the end it's bad for the sport.