It seems to me that it takes very little thought and research to realize that investing in science and progress is one of the good ways to get a positive and beneficial return on public spending.
I doubt that many politicians actually fail to understand that, it's just that they are more likely to get reelected appearing prudent and cutting on scientific spending is an easy way to appear prudent and conservative. It also has the added benefit of the continued war on science that is going on in the US.
The good thins is that the private sector and other countries seem to be carrying on the baton.