I think donations are somewhat tied to a tradition of giving back for education that is sometimes not ingrained culturally as well as immigrant populations having to prioritize their families first with later generations maybe then having more financial freedom to do so.
While I used to think that New Jerseyans tend to keep a tighter hold on their wallets and there may be some truth to that, I think a greater factor may simply be a culture of donating by alums at private vs. public schools.
As a partial aside, sometimes Rutgers' own are not the advocates they can be. Terms like "immigration (you probably meant 'immigrant') school" perpetuate misinformation.
Probably not nearly as many as you perceive are actual immigrants/first generation (more of those passed through in the 80s and 90s) or foreign students. Rather, many are already second or even third generation Americans. The U.S. overall, and especially places like New Jersey, are becoming more and more ethnically diverse as time goes on anyway, as those populations are expanded in subsequent generations.
Rutgers is not even at the top of the list of 'least white' schools (likely multiple U California campuses) even if it's likely more diverse than UMd, for example. Living down here in MD I would tell you from my observations that College Park is quite diverse and that's not just a recent phenomenon. One visit years ago may not have given you an accurate snapshot of the student body make-up.
As stated above, like Rutgers, UMd does not appear to have a legacy of many large donations prior to this point. Of course, this is a transformational gift from a foundation associated with the alum who was already one of the school's bigger benefactors in the past.