I think they did a few renovations recently, but ran out of money and couldn't complete what they really wanted to do, which was a full renovation and expansion of the stadium.
Phase II was much more ambitious, but we've never started it: https://www.vmdo.com/gmu-spuhler-baseball-field-renovation.html
More ambitious than what we currently have? I'm not really sure why they don't add lighting. I mean, pretty much any high school field has lighting, and most municipal fields at this point do, too.
I was told that it is due to an agreement with the homeowners association across the street not to adversely impact the residents. Perhaps, former Mason baseball player(s) like Five Two can comment on this.