Why does extracting a large file with MacZip cause Mac OS 9 to hang?

Why is it that I can perform multitasking when extracting .sit files with StuffIt Expander but extracting .zip files with MacZip causes Mac OS 9 to hang until extraction is complete?

In modern MacOS, the multi-tasking is controlled by the OS itself. It 'deals' out CPU cycles to the running processes.

Classic MacOS 9 used 'Cooperative multitasking', in which applications took turns on the CPU, and released control when they finished.

https://en.wikipedia.org/wiki/Cooperative_multitasking

'Good' applications would provide code to ensure that they didn't hold on more than they needed.