He already overextended himself by invading Russia. Sure he was ambitious but how could German command not have seen it was not only futile, but irresponsible?

Was it so that he could draw the US into a two front war with Germany and Japan? That’s the only reasonable answer I can come up with, although even that logic is flawed considering the fact that EVERYONE knew the US was a massive industrial power - dormant as it was at the time.