The thing that makes searching intelligent alien civilizations interesting. Is it just the question of how we could be the only existing intelligent species in the universe? We haven't got any evidence about the existing intelligent alien species but we don't know many similar stars like the sun. The question is how long we can search the existing alien civilization? Maybe we must search for it for thousands of years.
Maybe, we will make contact tomorrow. But the SETI program is offering the frame where researchers can test the new artificial intelligence-based methods. That can use to scan multiple radio frequencies at the same time. The thing is that the SETI program offers also information about quasars and other radio-astronomical interesting targets.
But also the SETI program has created models about the lifetime of the civilization. The key element for civilizations to turn to super civilizations. Is that the civilization can move to another star system. Or other planets when their star would turn unstable.
That thing requires the conditions that moving to another solar system is possible before the sun of those hypothetical aliens would burn their home planet to ash. If aliens can change their home star they will make them immortal. But anyway the time to advance to the Kardashev scale 3 civilization requires more than the lifetime of the sun.
But from hypothetical civilizations to the real world. Why we are searching for stars looking for alien life and calculating asteroids? The reason for that is that the stars are there. They are an exciting thing. And even if we cannot ever see alien cities. That search gives the data that can be used to find exoplanets and other interesting things.
One thing that we should remember when we are searching for aliens. Is that there is a long list of cases where "certainly they do not exist". The list of those things is very long.
Source:
https://www.space.com/why-humans-search-intelligent-alien-life-SETI
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