How come we can't prove there are aliens with all the technology?

because it is nearly impossible to locate planets outside our solar system and the biggest we can find are the size of jupiter and then we cant look at it we only know its there by watching stars very closely and watching for a fluctuation the problem is there is no way a planet sustaining life could be any bigger or smaller than earth. and we cant see if there is earth sizes planets around stars yet hopefully in the future we can. also we have only been sending out radio signals into space for 90 years or 80 years and its only around as far out a Sirius 9 and then we don't know if the signal is intact or is scrabbled by now. the truth is we may never find intelligent aliens unless they visit us. there is a chance to find bacteria on the planets and moons in our solar system. there have been cases of bacteria living deep underground and living in freezing conditions which means there could be bacteria on other moons. its not as interesting as finding ET buts it something