I see there are cheap indoor wall clocks that are syncd with WWVB. But can't find anything that use gps instead. I am wondering why? Are the receivers too power

I see there are cheap indoor wall clocks that are syncd with WWVB. But can't find anything that use gps instead. I am wondering why? Are the receivers too power hungry or the signals just too weak? I'd think going with a gps time sync would be a more future proof design.