That was a cold war era jet. Back then money was no object for programs like that. But who says that they're not still doing that? They have to have something going on in the deepest bowels of aerospace HQ.
Now that the Russians are allies and even lend a helping hand in elections in the USA, you just need a new enemy to be the focus of technological warfare development.
But it's probably a bad idea to romanticise wild and awe-inspiring vehicles like the SR-71, given their ultimate aim, which was to help facilitate the killing of humans somewhere else. But I do wish that sort of energy was still present in the space program. NASA feels hamstrung by risk aversion, and SpaceX is... meh. Plus Elon Musk is a total dick-brain.
Yes, yes, Artemis is happening, the next five years will be exciting, but it is happening too slowly. The last Shuttle's wheels stopped rolling ten years ago this July.