Software always has bugs that need to be fixed. It is never finished because it has an infinite number of ways it can go wrong. The same is not true for any of the non-software parts of software design.
If you're a software shop you should have everyone who doesn't write code on a contract and not be afraid to terminate them when the product is mature.
A software can only ever be mature for a period of time. Technology advances, work practices change, and your software should adapt to it. Imagine text editing stopped at Notepad, or image editing at Photoshop 1.
Also, your second paragraph leaks of Americanism and undoubtedly, people are happier and healthier with stable jobs.
Not only does that metaphor not hold up (is UX obsolete in your opinion?), it's absolutely false.
This is software after all - surely you're aware how throwing out the old solution and trying to build a "better" one results in a long slog of making the same mistakes the old team/product made and fixed (but could have warned you about if they were kept around).
If you're a software shop you should have everyone who doesn't write code on a contract and not be afraid to terminate them when the product is mature.