This statement is completely baseless, and you clearly haven't followed the MySQL developments of the last 10 years. It's ironic that around the time Sun was acquired, MyISAM was still a thing; MySQL has gone a long way since then.
Independently of a value judgement of "how good PGSQL/MySQL are" (I'm not making any implication in this sense), MySQL's development has been proceeding steadily, with no particular change (on the engineering side, at least). Oracle has actually put considerable effort both on the engineering and marketing side, of the 8.0 release (but again, I don't make any implication about the value of the products per se).
That's largely because enterprises often have big investments in SQL server, OracleDB, and/or DB2, and are only using open source engines for more lightweight purposes, and/or as part of cloud transitions where they are just taking vendor default options or whatever options was supported when they came on or longest.
At least, that's my experience working in enterprise and being literally the single voice urging even considering pros and cons before using MySQL-by-default with no particular rationale in a transition effort (which resulted in us using Postgres.)
I believe this has largely been driven by cloud - developers are now more able to choose the components they want to work with, instead of being told what to work with. There are of course plenty enterprises that are strict here, mandating cloud hosted SQL Server for example, but the general relaxation of constraints has struck me as a very pleasant surprise.
I've yet to come across MySQL being used in a cloud-based system, but I'm seeing Postgres more and more. When I do see MySQL, it's part of on-prem services that are considered "legacy".
What is the Galera-equivalent in the Postgres world? There's BDR, but the latest versions are closed source.
We use Galera in a bunch of places because it's fairly straight forward to get an HA cluster going, and with keepalived, we can point a front-end to a vIP that fails over automatically if one system goes sideways.
Like most software that gains adoption, MySQL made some very broad claims about their software's capabilities and never really delivered on them, at least not in a way that would be considered production-ready by Serious Persons(TM).
That's the crux of MySQL v. PgSQL, Linux v. BSD, etc. Good engineers spend their time building good software and are generally too focused on that to spend much time going around and making outlandish promises. Postgres has benefited from Oracle's intentionally-bad stewardship over MySQL, but it doesn't usually work that way.
Inertia is what I've noticed as well. The few people I've convinced to actually try out postgres have ended up liking it more than mysql.
In AWS, Aurora MySQL is almost always the database of choice, for just about everything SQL.
The added benefit of this is that you then know what software you're running, instead of Amazon's fly-by-night hackjob. We've hit several real-world bugs that were either incorrect backports of something that had been patched years before upstream, or wholly new issues caused by whatever they're doing to make Aurora auroar.
https://aws.amazon.com/solutions/case-studies/amazon-fulfill...
When I looked at Postgres, slightly earlier, I thought the same as you: how can anyone charge money for an RDBMS when this exists?
The great think about Postgres is it has huge momentum and the team are delivering new features. Maybe Apache has less momentum because it's matured and doesn't need much momentum.
From a momentum point of view I see Postgres as the biggest FLOSS project. I see no point in choosing another RDBMS right now. Time to short ORA stock