RealForce also has ABS space bar.
In days of old PBT was notoriously difficult to mold keycaps from, and larger keycaps used to warp, especially the space bar.
Thus most PBT sets have an ABS space bar as ABS does not warp anywhere near as much.
But these days companies seem to have resolved the problems, and now most PBT sets do include PBT space bars.