The Florida Brightline is limited to 125 mph. Also no grade separation which is needed for higher speeds. Generally countries use grade separation when speeds exceed 110-120 mph. California really needs the 200-220 mph to make the trip worthwhile so it needs to be grade separated. A lot of the work done so far in California is the overpasses over freeways and roads its crossing.

Brightline has had a lot of fatalities due to lack of grade separation.

https://www.miaminewtimes.com/news/death-train-a-timeline-of...

It's actually doing really well but it has not much to do with them being a red state and everything to do with them having an aging or tourist transit population that needs to get between cruise lines and theme parks.

Besides those cases there are not a lot of reasons to be transiting that route, or at least not nearly compared to the number of folks that would want to transit SF <-> LA. Totally different needs that are easier to address, and less pressure to prove out value / fewer digestible alternatives.