I think there are probably at least some alien civilizations in our galaxy, but at least one of the following conditions applies to each of them:
(1) They don't have the resources for widespread interstellar travel, so they haven't come here yet, and if they've picked up our radio transmissions, they may be far enough away that even if they were to respond (which they might not), the response could take a very long time to arrive and might not be detectable or comprehensible when it does.
(2) The intelligent civilizations that have spread through the galaxy have some pretty strict protocols about contacting pre-interstellar civilizations, and we haven't yet met the conditions that they've set for when they would reach out to a new species. They may also be deliberately intercepting any signals or other evidence that might prove the existence of extraterrestrials because they don't want us to know yet.
(3) They actually *did* visit the solar system at some point in the past, whether directly or through long-range probes, but humans had not yet evolved and nothing about Earth seemed all that interesting to them, so they moved on or they're still monitoring Earth as a relatively low priority. Just because they *could* theoretically establish outposts all over the galaxy doesn't mean that they *would.*
(4) They are very psychologically different from us, such that contacting other intelligent species simply doesn't interest them, or the balance between fear and curiosity is so heavily tilted towards fear that they actively avoid it. They may or may not be aware of our existence, but if they are, they either don't care or are actively hiding.
(5) Their physical forms are something we would have trouble even understanding as "life" because their biological processes are so different from that of any known species on earth, so they could be 10 million light years away or right next to us and we wouldn't notice the difference.