we havent discovered alien life because we can't detect it. we literally don't have the tech. all these exoplanets that ''might'' have life could be hosting dinosaurs and tons of living beings and we couldn't be certain.

what about aliens emitting radiowaves ? earth radiowave haven't traveled further than 60 years... low enough to still be in a potential containment zone and noisy enough to destroy any remnant of what we might have detected due to dispersion.

our spatial detection tech is shit tier. the resolution is terrible and odds are quasi certain that we can't focus on anything interesting in our neighborhood

hell there could be one behind you right now and you wouldnt even notice...