The "Get rich and get out" expectation is in place because working at the pace that lots of SV companies demand creates an unacceptably high risk of burnout. To compensate for this risk many workers and entrepreneurs have setup a mental and social framework of "I'm only doing this until I can retire young".

Of course, early retirement happens for vanishingly few workers. Some companies go Google or Uber and let the founders retire, but most do not.