Look up the hull loss numbers on the SR-71. More than a third of them were lost in incidents despite never making contact with the enemy.
It was also insanely expensive to operate: $300k/hour in 1990 dollars, and there aren’t reliable numbers on development costs with all of the black budgets.
33 percent attrition and could only fly once a week.
I know satellites and drones have replaced the sr71 but it would be cool if someone would build a plane as capable again.