Space advocates only make up a tiny percentage of the electorate
So, we have very little control over who gets elected. It takes a lot of votes to elect someone, be it to Congress but even more so to the White House.
We can "afford" lots of things, but that doesn't mean we'll get them when it comes to the battle of the budget. The policial process is largely geared to use the budget to buy votes of different voting blocks. There aren't enough space buffs to worry about, so the budget remains about the same year after year.