There can be various conditions and factors that might lead an advanced civilization to focus on interstellar travel without colonizing other planets in their own solar system or even their own moon. Here are a few possible considerations:
Limited resources: The civilization might have exhausted the available resources within their own solar system or found them to be inadequate for sustaining a growing population. This could motivate them to search for new resources in other star systems rather than investing in colonization efforts closer to home.
Uninhabitable local environments: The planets and moons within their solar system might possess extreme conditions or lack habitable environments. For example, they could have hostile atmospheres, intense radiation, extreme temperatures, or no readily accessible sources of water. In such cases, it might be more feasible for the civilization to pursue interstellar travel in search of habitable or more suitable environments.
Technological limitations: Although the civilization has developed advanced interstellar travel capabilities, they might still face significant technological constraints when it comes to establishing sustainable colonies on other planets or moons within their own solar system. The challenges could include issues related to terraforming, adapting to local ecosystems, or creating self-sustaining habitats.
Preservation of the home system: The civilization might have a strong cultural or ethical principle of preserving their own solar system as a natural or historical heritage site. They may view other celestial bodies in their system, such as their own moon or planets, as important scientific or cultural landmarks that should be left untouched and protected. As a result, they focus their colonization efforts exclusively on other star systems.
Unique scientific or strategic objectives: The civilization might have specific scientific or strategic goals that are better served by interstellar exploration rather than colonization within their own solar system. This could include studying unique astrophysical phenomena, exploring distant exoplanets, or seeking contact with other intelligent civilizations.
It's worth noting that the motivations and priorities of advanced civilizations can vary significantly, and these factors are purely speculative. As our understanding of the universe and our own capabilities continues to evolve, the approach and priorities of future civilizations may differ from what we can currently imagine.