As noted by a post above SQL is not a composable language. That means new features can not be implemented as (standard and user-extendible) libraries. And that makes the standard more bloated with every new feature. The DB-vendors benefit from the situation because it gives them more customer lock-in because when the standard is bloated, not everybody is likely to be fully compliant with it, which causes customer-lock-in.

Somewhat ironically the standards-body also benefits from such bloat because that is the product they are selling. The bigger the standard the more money they can ask for it.