If these reflectors were not required, then why can't any observatory today reflect lasers off the surface every time? A few photons may indeed return after many attempts as MIT did, but not regular enough for the required data. Secondly, any returned photons from the general surface won't give accurate positioning, just a general return from somewhere. The exact point, altitude etc is needed for computational experiments. Go to such an observatory and ask. There are dozens around the globe. I have attended four of them so far.