The answer to your question is VERY simple. Mooney is the coach!
Mooney's career .550 winning percentage tells us all that we need to know. He can barely win 1-2 games at a school that provides well above average opportunities. Often repeated, but true, UR has a great basketball tradition, pays their coach really well, provides a terrific arena, invests in upgrades (like the practice facility), and has fans who come to games and support the team.
There is NO REASON why a decent coach shouldn't be winning big at Richmond! Tarrant & Beilein proved the hypothesis in the recent past. If Mooney were at a program with lesser benefits, I am willing to bet that he wouldn't win more than 30-40 % of his games. Of course, that skill level gets a coach fired in 2-3 years.
If you seek a more definitive explanation to your question, there are many technical reasons why Mooney is a low average coach. Some examples include:
1) Well below average bench coaching skill. He is one of the worst at this that I have ever seen. I grew up learning from Adolph Rupp, Denny Crum, Bobby Knight, Digger Phelps, and Rick Pitino. Mooney isn't even near the same ballpark, and he has proven it time-and-again. The data (specifically losing so many close games that could of, or should have been wins) over 18-seasons is proof that the problem isn't a coincidence, bad players, or bad luck
2) Well below average ability to manage personnel. Mooney has a LONG history of teams in disarray because he can't figure out which players should be on the floor together. The evidence (multiple occurrences over multiple years) is extensive. This year, his playing combinations involving Nelson, Quinn, Roche, Grace, Bigelow, Bailey, and Noyes have helped to create the bumpy road. Mooney frequently doesn't use the right personnel at the right time. Again, a LONG term problem, this year isn't the first that this has been a significant team issue
3) Rigid and risk averse. Ample evidence shows that Mooney most often makes decisions based upon long-held historical beliefs. This includes his use of timeouts, and his choice of offense and defensive schemes. He repetitively pounds the square peg into the round hole. He is not good at adaptation, he prefers to do it his chosen way whether it is working or not. He is not good at making decisions on the fly (changes dependent upon evolving circumstances). Again, repetitive examples over the course of many years
There is much other evidence, but, these are the most flagrant in my opinion. So, the answer to your question is simple; Mooney is the coach.