In these trying times professional customers buy most of the available stock anyway, but there is more to it.
A major reason to leave private customers to specialists (e.g. certain distributors) in general, would be low return on effort and customer protection laws.
There is the argument about satisfied private customers acting as multiplicators. Again, those can be served by the distributors. In rare cases, say the recently introduced ADR1000, ways can be found to supply private enthusiasts with components.
This whole topic takes me back thirty, forty years, when a private customer had to do with components sold by distributors. In contrast, today that customer has the option of shopping worldwide. One can only assume that certain companies are willing to sacrifice business, for the benefit of not having to deal with a certain type of customer directly.
Edit: spelling