You can see a break-down of the core team and major contributors here, as well as their current company affiliation: https://www.postgresql.org/community/contributors/

(and as noted in the other comment, whilst EDB certainly makes important contributions, they are one of many)

TIL Julian Assange was a contributor to PostgreSQL

3 of 7 work at EDB, and the core team doesn’t drive the project roadmap. And EDB hackers fail to get patches in all the time, just like everyone else :)