It doesn't feel like this applies here. 6-7 years ago a decision was made to go with stored procedures over using an orm or at least implementing db logic in the application code.

Along with this, they also chose to split the responsibility for code and sql across two teams.

6-7 years ago, plenty of other options were available. In fact, the sharded MySQL solution that they use now was already possible back then.

It sounds more like they made some architectural decisions based on the companies org chart and it came back to bite them in the ass hard.

edit:typos