I think the simple answer is philosophy of Kaizen(改善)- continuous improvement. I started working with postgresql when it was just postgres95. Recently found that my earliest question on postgresql-users was 13th October 1998, 20 years ago (https://postgrespro.com/list/id/3.0.2.32.19981013214318.0069...).

I still use PostgreSQL in my startup for almost all critical production workload. This in itself a testament to its improvements. I remember I starting with c libraries of msql and postgres95 and continued to work with them as they evolved into postgreSQL and a new kid on the block mysql. I liked postgreSQL due to its adherence to SQL. Since I like working with relational algebra. So even though MySQL was more popular in later years, I still used PostgreSQL more often, except for building qmail servers with mySQL backend.