I would love relational database engines to adopt the same syntax when they support a feature. There is no compelling business case for them to do so though. Browsers converged largely in response to IE's dominance. If Firefox, Safari, and Opera had each gone their own way, no single one of them could ever get enough marketshare to get developers to care. Together they made a block significant enough that Microsoft was forced to join in or die. (Actually did effectively die once Edge was moved to the Blink engine. Now it's a satellite of a mostly standards-compliant effort.)

But databases aren't browsers. Devs just have a single target usually: whatever database engine the company decided to use.

Still it would be nice to have greater overlap to reduce the niggling details between them that only seem to exist today due to inertia rather than technical necessity.