Larry Dighera writes:

Why?

They might total the airplane that you share. They might not maintain it
properly. They might damage it without telling anyone. There are many
possibilities.

It requires that they be responsible adults, preferably business
people who can afford to own 1/3 of an aircraft.

Many adults aren't that responsible. Pilots get themselves killed often
enough; why would they be any more cautious for someone else's sake?