Re: It's the monocolture of open source that led to this
Ok, I think you're being a bit revisionist in your history....
In terms of Open Source... take a look at Apache.
There are so many competing project that have overlap. In the big data space, as an example, you have Ranger and Sentry. There are other examples and that's just Apache. There are now competing stacks that sit outside of Apache control.
So its a bit disingenuous to say 'one anoited all'. What I think you're seeing is the survival of the fittest. (Looking at Open Source browsers)
With respect to Eclipse... If memory serves, its based on Rational Software (Rational Rose) that IBM bought and couldn't deal with it so they tossed it over to the Open Source community. Also cloudscape's silver cloud became derby / javadb.
What the open source culture did was to skew the model for commercial code. I agree that the open source model is flawed, but not for the same reasons you suggest.
Also I don't know how old you were way back when, but while you saw competition, if you followed the path of evolution you saw the market choices shrink. Take a look at the whole spreadsheet market as an example. Visicalc, Lotus123, and I forget how many others that disappeared early on. Relational Databases? (Progress Software, Informix, Sybase, Oracle, IBM, and many more ...) How many are still in use today? Most have been supplanted w mySQL / MariaDB, even derby/javadb has a niche.
Sorry, just keeping it real.