Fandom is by its nature irrational (in fact humans operate mostly on irrationality despite our pretenses otherwise and regardless of what the subject might be). The same irrational hope often happens to those who constitute what we might term diehard "negavols." The only time it doesn't happen is when you've truly quit watching football or a fandom. And even the most pessimistic among us still watch the games on tv.
Those who don't watch til the end are often the most susceptible to the sucky emotions of losing. Hence, the attempt to be so negative that you find yourself attacking fellow fans for even expressing a slight glimmer of hope. Pessimists don't want to catch the 'hope' bug for fear of being let down. It's a matter of emotional self-preservation. And though it's hard to be hopeful even if you're an optimist in general, it's difficult not to have the game time experience you describe even if you temper expectations or go into thinking we're gonna lose.
There's a reason that according to myth, Hope was trapped in Pandora's Box and it was the release of Hope from this trap that was considered such a curse to humans.