I thought there were nightly (or at least daily) builds? At least it looks that way in the WebKit archive where the three latest builds right now are:
262503@main
April 3, 2023 at 01:23 PM GMT+2
262502@main
April 3, 2023 at 10:51 AM GMT+2
262501@main
April 3, 2023 at 10:17 AM GMT+2
https://webkit.org/build-archives/#mac-ventura-x86_64%20arm6...
A large part of the post's complaint is that not only does Safari not have a nightly build, but they don't even give advance notice of when their "technology preview" (beta) or stable releases are coming.
Chrome, by contrast, not only has a public schedule, but a public dashboard where you can follow along.
https://developer.chrome.com/blog/early-stable/