Indeed.

> why isn't it a standard feature of SQL to just compare two tables?

Not enough people have complained about needing it (it doesn't hit the desired ROI for a PM to prioritize the feature request).

SQLite's SQL Diff I first came across years ago - super useful. It's the perfect example of the industries which pop up to fill in the gaps that huge software vendors like Microsoft leave open. I used to work at a company valued at hundreds of millions of dollars, which made nothing but such products filling gaps.