Anyone with a large python 2 codebase is going to want to stay behind if they could.

People still run old FORTRAN from 20 years ago in production. I'm sure some old COBOL code is out there. The reality of not wanting to re-write working code is somewhat real.

This is such a good analogy, and really highlights the point that python 2 stalwarts look at organizations hiring for FORTRAN and COBOL today, and say to themselves, "Yes, this is the kind of organization I want to build." An organization that will either (most likely) be completely irrelevant in 10 years time or have to pay a massive premium salary for any engineer that can maintain their systems.

Not only are there scientific disciplines where modern Fortran is still dominant, but there isn't much of a salary premium for working there.

And people said what you said about it 10 years ago. And 20 years ago. And 30 years ago.

When those folks want to do scripting, they mostly use Python. And they mostly use Py3, from what I can see.

Are people routinely still purposefully writing new code in 20 year old versions of FORTRAN, or just maintaining existing stuff?

it's not on purpose, it's out of necessity. For example, a company has a huge COBOL code base. It plans to migrate to say, python. After 2 years of analysis, and some failures, they realize how much their organisation is driven by the software. So they decide to change their business processses. Another two years of analysis. Now they start rewriting again. After one year, they realize the consluting company responsible for the rewrite is screwing them, they stop the effort. New management comes in : "we need to put more resources in marketing, so we put all IT efforts on hold for two years". Now marketing needs data about its customers, so they ask the IT team to build some reports. This implies coding new stuff in COBOL, after 5+ years...

That's what I'm in right now :-)

Back when my startup had a Fortran compiler as one of its products, most of our customers were writing new code in modern Fortran, and modernizing old code. The folks who were just running what they had without updating it probably were using g77 or another free compiler.