Honestly, why would they? If there is a product that does what they need, why spend resources improving another.
Just because it's open source and they could spend money improving it, doesn't mean a company will spend that money improving it.
I would hardly say MySQL does what they need without any improvements. They built an entire second platform on top of it.
https://eng.uber.com/schemaless-part-one/
[0] https://github.com/facebook/mysql-5.6
https://dom.as/2016/08/03/mysql-does-not-need-sql/
Honestly, why would they? If there is a product that does what they need, why spend resources improving another.
Just because it's open source and they could spend money improving it, doesn't mean a company will spend that money improving it.