Even if they do not strike gold the second time, there can still be a multitude of reasons:

  1. The innovators will know a lot about the details, limitations and potential improvements concerning the thing they invented.
  2. Having a big name in your research team will attract other people to work with you.
  3. I assume the people who discovered something still have a higher chance to discover something big compared to "average" researchers.
  4. That person will not be hired by your competition.

5. Having a lot of very publicly extremely highly paid people will make people assume anyone working on AI there is highly paid, if not quite as extreme. What most people who make a lot of money spend it on is wealth signalling, and now they can get a form of that without the company having to pay them as much.