Because "existing" thorium salt tech is even more experimental than the designs various companies are working on.
Because HALEU fuel is intended for (a) reactors with higher power densities which is antithetical to breeder reactors and (b) reactors with longer cycles which is antithetical to salt coolant.
Because Th-232 is a fertile isotope, not fissile, so it doesn't actually help you run a reactor until you have already been running for a few years (i.e. you're gonna need uranium fuel to start your thorium cycle).