Because these stars are nearly all GIANT stars several hundred times brighter than the Sun. For example, the absolute magnitude of the Sun is about +5.0. A giant star has an absolute magnitude of 0 to -2.0, and at a distance of 10 kiloparsecs you get an apparent magnitude of at least -2.0 -5 + 5xlog(10,000) = +13.0. Some stars are intrinsically brighter than this. The masses of these stars are only about that of the Sun.