Well, at first I thought about the Hubble program, and the budgetary cycles that impacted it through its development and build phases that caused a lot of its problems.
OTOH, look how long Pioneer 11 and Voyagers 1 & 2 lasted...
I'd bet the older technologies were more resistant to the rigors of unprotected space. The processor chips used sapphire-on-silicon technology.
Look at the B52 and A10, but they along with the early space probes didn’t take decades to become operational.
Concerning the Hubble, I read here on FR that it’s based on the Keyhole spy satellite and that it would have been much cheaper to launch new replacements than to do service missions with the Shuttle.
And then there is the James Webb space telescope...