That was so Parallels could take advantage of all MacOS Big Sur's revamped features, plus add more than 30 new features.
The big changes in the latest MacOS Big Sur meant putting in the equivalent of more than 25-man-years of engineer programming time deep 'under the hood' at the kernel level. This time around, it was a huge rewrite for the Parallels engineers. Parallels gets updated every year to keep pace with Apple's major OS upgrades. You can download Windows and various Linux distros from within Parallels and run them at the same time on your Mac.
