Press on Vinyl are able to make there own masters. Can you clarify what you mean?
Normally "masters" are lacquers, though, so a company that makes their own "masters" still probably outsources the steps after the lacquer and before stamping finished records.
> With the destruction of Apollo Masters, producing lacquer discs fell solely to a small Japanese company, MDC. This caused a significant strain on the industry, as Apollo Masters was responsible for 70-85% of lacquer production.[4][5] As a result of the strain, orders became backlogged and delayed, (...)
> With a decrease in lacquer production, some vinyl pressing plants turned to alternate means of producing records, including direct metal mastering, a costly method of producing records with copper instead of lacquer.