Presumably ego-stroking, or at least the patriotic equivalent thereof.
I mean space related ventures are expensive. There's always progress to be made. Imagine if we never got cars to drive up to 100mph because they cost too much to test drive. I imagine theres similar optimizations that need to be done with rocket science. If they never get to test them in real space missions then they cant improve.
If Trump throws his personal money at the researching and funds that'll be great.
That's a bad example since you don't even need to go that fast. ---