Supermassive blackholes reside in the center of galaxies which have higher density of matter / stars. Quasars are very distant and thus very old images of those

Supermassive blackholes reside in the center of galaxies which have higher density of matter / stars. Quasars are very distant and thus very old images of those galaxies from the time they were "cleaning" the area from surrounding matter. Milky way center was likely a quasar a long time ago as well, but it already passed this "cleaning" phase and there isn't much floating matter in the center anymore.