I'm curious why you think it is that slow?
In the time frame you're talking about, and given that you've broadened the scope to include vast budget government projects and one off mission specific craft, then doing the same with cars, we've gone from steam power in a few miles an hour to petrol, diesel compression engines, hybrids and pure electric power, rocket and jet power. We've seen Mach 1 exceeded, and 1000 miles an hour on the cards soon.
On another metric, we've seen real world ownership costs plunge. We've seen safety (the built in type) increase beyond all recognition.
Electronics have played their part in safety and ease of use, making many of the old chores a thing of the past. We've seen the working life of ordinary vehicles, available to the average man in the street double and treble in just thirty years or so.
Fully autonomous vehicles are out there and testing now, and have been to various levels of sophistication for a few years.
There are of course things that slow down the adoption of new technologies, all sorts of legislation for safety etc.