Postgres's whole origin story is basically to think outside the box and don't be constrained by existing thinking. Stonebraker thought existing databases were too limited in terms of their data types and expressiveness. He started Postgres as an evolution of Ingres (Postgres = Post Ingres) that added rich custom data types and a rewriting system based on rules.

Columnar and all the other fun stuff (JSON, GIS, inverted indexes, embedding vectors) is a natural progression of that thinking. With TimescaleDB, Hydra, Citus, pg_mooncake, etc. becoming very popular the last few years, there is a clear demand for an integrated experience.

(Stonebraker also thought one database shouldn't do everything, as described in his early 2000s "One Size Does Not Fit All" paper, and Stonebraker branched out into HStore/Vertica for columnar. In hindsight, I think that was appropriate for the time, but no longer a significant concern.)