Thing is, if aliens *do* exist, we might not meet them but we *should* have seen some sign of them at this point.
Consider this - what is the precursor to colonizing space? Exploring space. And what's the precursor to exploring space? Surveying space. Assuming sentient aliens reason in a manner similar to us, they would likely want to conduct an automated galactic survey once they had the technology available to do so. This would consist of building autonomous, drone-crewed vessels that would travel to new solar systems, conduct orbital surveys of any planets to determine if any of them either had life or had conditions suitable for life, then construct an outpost on one in order to build a facility that would construct and launch several new survey ships to repeat the process. It sounds futuristic, but by most estimates we're within ~100 years of having the technology suitable to conduct such a survey ourselves - it would take tens of thousands of years to complete such a survey on a galactic level, never mind trying to explore other galaxies, but once started the survey would need very little additional input/oversight from us and within a few millennia, we'd have an intergalactic survey and communication web set up.
That sort of a timescale is the blink of an eye in the cosmic scale - if dinosaurs had developed sentience and intellectually progressed at the same rate we did, they could have had that sort of a system up and running less than 1% of the way through their time on this planet.
So, realistically, we should have seen *something* in our solar system from extraterrestrial sentient aliens, if they indeed exist in our galaxy - probably not them in person, but maybe a waystation or automated communications satellite of some sort. That we have seen nothing lends credence to the idea that we truly are alone.