Pure race long term survival, any sane civilization knows very well a single space item hurling fast enough can wipe out all conplex life on planet. Or vulcanoes, tectonics etc. Also every star eventually goes down, usually pretty violently (but thats properly a long term concern).

Its not 'if' question, just 'when'. You cant be space faring civilization and not know this.

Most of the theories assume that aliens want to spread out as much as possible. But perhaps they are satisfied with a second star system as "backup"?

Maybe they even live inside asteroids or ships orbiting a dwarf star, because they are mostly in a Matrix-like existence and don't have much of a physical life?

If someone provided a matrix world where you could live your dream life, I think a lot of us would choose to live in it. It would be so much better than real life. Our physical bodies could be maintained by robots, providing us with the perfect mix of sustenance and physical exercise to increase our life spans. Your body would eat healthy, but your mind would experience whatever food you would like.