It seems that in the "earlier" versions of a new Mac OS, such beta releases happen faster. But as the OS matures, they come later, and eventually stop.
According to
MacTracker Sierra, High Sierra, Mojave, and Catalina were launched in late September and early October with updates the last of October, early December, late January, late March, May, and July, Catalina had an additional release in September, probably due to the delayed launch of Big Sur pending the availability of Apple Silicon Macs. So, it would seem, Big Sur is pretty much on schedule If you factor in its late launch. The subsequent version in each case was previewed at the World Wide Developers Conference in Early to mid June and beta tests were in full swing before the July update and most of the beta testers and the bulk of the OS development team had transitioned to the upcoming version. I will not be surprised if are were only five MacOS 11 updates, assuming MacOS 12 makes the normal last week of October, first week of September launch date.
So in essence your adoption decision is driven by the calendar and Apple's carefully orchestrated development/support schedule.
