Remembers, the millions spent on space exploration are not thrown out of the planet window to literally space! They are spent right here, given to people and making them work.
Instead of having PhD working at McDonalds, (and having less qualified people on unemployment or homeless), you would have PhD working to explore space, and less qualified people working up the jobs PhD don't resign themselves to do.
But there are two more probable reasons:
5) Aliens said: NO.
6) You don't really believe those billions of dollars were wasted on the F-35 program do you? (And all those other waste military development programs, of which we will never know anything about given the ACCOUNTING files have been destroyed in the 911 attack on the Pentagon and WTC-fucking-7). No, all this money has been used in secret space travel and weapon development programs, and they already have interstellar space ships and people going out there.