It's because Python tends to be the most common programming language for startups due to being easy to hire for, having good library support for a wide range of use cases, being good for web development, etc. And MySQL is focused on catering to enterprise customers who don't use Python. The last time I heard, they had something like one person working part time on Python support, so the drivers weren't nearly as reliable as the Postgres tooling.
Python has had rock-solid, widely used MySQL libraries for well over a decade. I've never seen evidence that MySQL and Python aren't a strong (and popular) combination.
Not the most sound method but I was demonstrating the relative popularity of programming languages to my SO the other day using find in the Who's Hiring thread for May and python was the most popular.
A ton more companies have some Python scripts than Python as a primary development language; this skews naive keyword matching assessments of job postings.
