We don't need another flame war here.
And yes, most of the web is build on Wordpress/PHP - but you don't need to be a developer to install Wordpress.
I'm just stating what I believe to be a fact: that the majority of web developers in this world never think of PostgreSQL as an option. I don't care whether that's a logical thing for them to think. It's just a fact, whether I like it or not.
If you think I'm wrong about the facts, please feel free to open a phone book in any part of the world other than the Bay Area, call up a decent sample of people who self-identify as web developers, and find out what percentage of them have ever heard of, let alone used, PostgreSQL.
I'm just stating what I believe to be a fact...
It's just a fact, whether I like it or not.
(I happen to agree with your opinion, but the semantics here bug me.)
Anecdotal evidence: I've interacted with dozens of other people who call themselves web developers over the years, and most of them (outside of Silicon Valley) have never used PostgreSQL, nor any advanced features of SQL in any other RDBMS.
Objective evidence: the large market share of WordPress, Drupal, and other content management systems that don't use any advanced database features; as well as the large market share of frameworks such as Rails, Django, and Laravel that encourage developers to stick with the ORM and not care about advanced database features.