> unimaginable amount of technical debt

"That's life" in the RDBMS space. All of the major vendors are drowning in tech debt and there's (almost) nothing they can do about it because of backward compatibility limitations.

For example, Microsoft SQL Server 2025 will create new databases with default settings that are unchanged from SQL 7 -- from the previous century!

Requiring backward compatibility doesn't imply the code quality needs to be low. Nothing prevents them from improving their code base except the organization itself - the incentives, promotion driven development etc.