This issue has been long debated for years well before I started playing tennis (in the '00s) and here's some of the issues. @perfectchaos007 feel free to correct me on any of these statement as I believe we both have seen many of this during our prep years.
The first general issue is publicly funded programs giving scholarships to foreigners. If I'm correct, UT's athletic program is sustained financially by itself and is thus not reliant on tax payers money. TCU is also a private university. So if we were to ban or limit foreigners on athletic programs that are publicly funded, there would have been no effect on today's teams.
Limiting the number of foreigners on ALL college team is also not that great of an idea. It's so not much of an issue at programs like UT or Florida but it will be an extreme problem for the mid major teams like Stephen F Austin, New Mexico State, Wichita State, etc. trickling down to the NAIA and JUCO levels. The thing about tennis is a lot of American players are from well to do families and do not need help both financially and academically to get into colleges. A lot of junior tennis players would rather walk on or play club tennis at a big name university rather than play tennis at a school three hours away from a major city with a student population the same as their high school. I know numerous friends and other people who were rated 3 or 4 stars that would have been great players at Southland schools and the DII level instead go to a big state school for more of a traditional college experience. The traditional powerhouse high school girls tennis program in Texas is Highland Park but most of the girls don't take scholarship offers (compare this to Katy High School football, Abilene High Volleyball, Duncanville Girls Bball).
JUCO tried to limit the number of foreigners in 2012 only for them to be sued and have the regulation repealed in 2015.
Coaches also LOVE to recruit foreigners as they're seen as more reliable than Americans. Foreigners are more likely to commit right after their official visit and not string coaches along and flip like Americans. Also foreigners are quick fixes. When Fendick McCain was having trouble filling her roster, she was able in a span of several months to convince an international to take her exiting exams, graduate, and come to UT a year early. Joffe has turned every program he's been at (Ohio, Maryland, A&M, and now UT) into conference leaders because of his ability to recruit and get foreign players to play for him at struggling places.