Think that Rubin's decision to stay or go largely depends on whether he could declare and be a top 150 (or even top 100) player almost immediately. If not, being a pro tennis player is awful. Those below the top 150 (and sometime even below the top 100) are forced to play a bunch of satellite tournaments for money that often does not even cover expenses against Eastern European, South American and Asian grinders that no one has heard of. If that is the alternative to WF, staying in college is the obvious option. Not only does the money suck for those outside the top 100, but literally no one goes to those satellite events -- friends and family -- if that. College tennis matches look like Wimbledon by comparison. Also, the life sucks as those events are always in remote locations, and unlike team sports the players often travel alone, stay in modest accommodations (or with host families).
I'm sure that given Rubin's growing reputation he would get some wild card entries into ATP events, but Rubin only gets to stay at the level and get paid if beats some really talented men. He is not playing the #1 player at Elon in pro tournaments. So, even if he decides to make the jump because he has invites lined up, there is no guaranteed payment. To get paid, Rubin has to beat the best... If he is not ready to do that, another year of college makes a lot of sense.