There is a good reason for that. In order to have an amalgamation of systems with design life of a given duration, every component must have a design life of much, much longer. When you get lucky, a system can go for a really long time relative to its design life.
Great examples of this are Spirit and Opportunity. The latter failed at ~61 times its specified design lifetime.
Having been a small part of some space-mission design and larger science collaborations, I can state with confidence that you really don't want your subcomponent to be the one that causes a failure.
And Voyager 1 and 2 are still zooming as far away from our solar system as they can get and happily sending back teeny bits of data every now and then. Pretty wild to think their voyages are now over 40 years old.
For a lot of stuff there's redundancy too— like rovers with six wheels but that can drive with any four, and the Curiosity and Perseverance missions having dual computers and dozens of cameras. I'm sure they run scenarios where significant chunks of the rover's systems fail and they figure out how to carry on anyway— thinking in part here of the famous HGA issues on Galileo:
Great examples of this are Spirit and Opportunity. The latter failed at ~61 times its specified design lifetime.
Having been a small part of some space-mission design and larger science collaborations, I can state with confidence that you really don't want your subcomponent to be the one that causes a failure.