My son’s swimming coach is a triathlete and we’ve talked about it. Lots of barriers. For one, at least in Michigan, there isn’t really an appropriate high school season. Spring and Fall seasons both feature snow in much of the US. Much harder to organize something in the summer.
What he has done is organize one week tri camps with the idea of doing an onsite race at the end and then a local race for those interested. Most of the interest was from elementary and middle schools kids, very little interest from the high school students.
I think the best you could hope for would be to start a club and then encourage surrounding schools to start a club. They could train together and race existing races. Maybe once this was active at several schools you start put on specific events. I think it would be a very long path to a varsity sport.
TCW