Interesting point; I didn't consider that. A civilisation with advanced enough technology and (by our standards) infinite amounts of time and resources could i

Interesting point; I didn't consider that. A civilisation with advanced enough technology and (by our standards) infinite amounts of time and resources could indeed have groups of individuals seeking exactly that. Still a far cry from founding galactic empires, but a reasonable motivation that I haven't really considered thus far. Such reasons for expanding outwards would, however, match our observations (or specifically lack thereof) perfectly: groups that seek isolation or refuge from their parent civilisation likely wouldn't bother broadcasting their existence to everyone or build easily detectable solar system-scale mega-projects like Dyson Swarms.