What is the difference between Apple's “Safari Technology Preview” for the public and the Safari beta download for developers?

Question

It is my guess that the Safari Technology Preview (STP) is updated less frequently than the Beta for Developers (BD).

I wonder if Apple publishes an explainer on the differences between the two, apart from the observable update cadence difference, and the marketing to different audiences.

April 15, 2021 - I see that the last BD release was on April 6, 2021. I speculate that STP was last updated in early March 2021 based on the tickets in the release log.

Safari download page