AFAIK such galaxies are ancient amalgams of many galaxies that have over billions of years collided and fused into the giant ball you observe. Due to the sheer size and therefore age of such a structure it is presumed that star formation in such galaxies is dying out, or even close to being extinct. For reasons why the core of the Milky Way is deemed unsuitable for life such large galaxies would posses huge volumes of space where life as we know it might find it hard or impossible to exist.