I am not sure I doubt that there is life elsewhere in the universe. But I don’t see any point in spending billions of dollars to show that there was once bacterial life on Mars. They sure aren’t going to find complex life on Mars. We will never actually meet space aliens. Even if there were intelligent life in the nearest star system from the sun, neither we nor they could ever traverse the distance. The best we could hope for is to communicate with radio.
Why such a putative society would even want to try — much less send aambassadors — requires ascribing human motives to it.
If they could find even simple life forms on Mars and see how they were different/similar to life on Earth, that might provide some clues as to how life came about.
Also, the more places they find life, the more likely there is life throughout the Universe.
Until they started seeing planets around other suns, we could only surmise how many planets there might be in the universe. Now we have a pretty good idea. Maybe we won't be visiting them soon, but it is something that is nice to know and keeps the scientists busy doing things other than screaming about global climate change.