Some items absolutely are zero sum - anything that is in short supply with a high demand becomes unobtainable for anyone who isn't rich.

Some things that are effectively out of reach for at least half of everyone:

  Mansions and Luxury Condos in desirable locations
  Private Jet
  Private Island
  The best quality food
  2021 Ferrari 812 GTS
  The best legal advice
  A favor from a US Senator

These things are effectively zero-sum, only a limited number of people can have them and we can't expand the supply very much (or intentionally don't because that would hurt their exclusivity value).