Maybe its because they're unsafe to use? IMHO, three piece bolt-together wheels are race-only and do not belong on a heavy street car. Hall made some in their 'Ultra' line for Panteras and now a decade later, the inner halves are cracking circumferentially under the inner bead. The most likely part to let go is the inner rear half as that's the highest load area in a Pantera. It's also one of the less easily inspected for cracks. The small shop that made them for Gary has passed on as has Hall himself. There are no spares and no one to call. The aluminum alloy used to spin the halves has proven to be not weldable. EVOD Industries in So-Cal can make up individual halves that fit; they will be stamped 'RACING USE ONLY'. I've sent three owners of cracked Ultra wheels to them and the new spun part is NOT cheap!
I've also been present when riveted-together three-piece Centerline drag race wheels have broken catastrophically at tracks. With those wheels, the lightweight centers, never designed for cornering loads, broke the lugnut center free of the rest of the wheel at speed. The rim, half the center and the tire passed one car on the track while the driver became very, very busy. Use ANY 3 piece wheel on the street at your own risk!