Having been involved in enterprise related technology at the time, I can tell you that there were a number of factors, some of which I think may have been allud

Having been involved in enterprise related technology at the time, I can tell you that there were a number of factors, some of which I think may have been alluded to here. * MySQL was looked at as cost effective and fast data store for developing less than mission critical things like backing web front ends; and back then much of the web work was really less than mission critical for a lot of organizations; this meant that so long as it was fast and didn't burden these new "web developer" types with too much ceremony, it was a compelling choice. Postgres of that era even then boasted a much better and more "correct" set of features that would appeal to enterprises, but wasn't all that fast and did bring that extra effort that most of these reckless developers on the fringe didn't want. * For enterprise work, Oracle, DB2, or to a lesser extent MSSQL where the choices. Open source was distrusted (what do you mean "free", what's the catch? Must not be worth anything if you can't charge for it. Nobody got fired for buying IBM, MS, etc). So the people that would most likely look at the trade offs in Postgres of that time favorably were the ones least likely to entertain it. The innovation was on the web side of the world, and there I go back to my first point. * PHP was also a big deal back then. Our company was convinced by one of our sysadmins to let him greenfield a help desk application for our internal support (~1997/98). PHP was the obvious choice because it was so easy and fast to write code that worked and was web focused... and the default database choice was MySQL. (We went way out on a limb and installed it on this new OS called Linux, Slackware if I recall correctly). PHP and its good support of MySQL as data store made it the default choice. Postgres wasn't even on the radar or a discussion point. * MySQL was developed by a consulting company with an interest in promoting it. Postgres didn't have that kind of directly interested marketing support. Sure you could get the code and install it, but there really was no marketing as compared to MySQL. So, easy to use, relatively friction-less technologies; targeted at really and an new technology industry that was just starting to take off; and that the concerns of that new industry didn't match up well with the strengths and weaknesses of the Postgres you could get back then, but did match up well with MySQL.... yep, I think all of those are reasons why things turned out as they did. BTW... I say this as someone that was never terribly fond of MySQL and still not. Back then I was an Oracle guy, since about Postgres v8.0, I've been favoring Postgres.