Big tech companies operate at the edges of the problem space. As a theoretical example, if you need to ingest and process 10TB of numeric data every day, you ca

Big tech companies operate at the edges of the problem space. As a theoretical example, if you need to ingest and process 10TB of numeric data every day, you can probably find an existing DBMS that you can tune to do this. But what if you foresee your volumes growing to 100TB? No one has needed that before. Patching an existing DBMS means your changes have to mesh well with all its other features. And since you have a lot of talent on payroll already, it's probably easier to write a DBMS that solves your narrow use case, but solves it 100%.