Apple's Mac machines are preferred by many for their relatively low-frills approach to computing compared to Windows. That doesn't mean they're impervious to common computing hiccups, though, such as unexpected system freezing or spells of unresponsiveness. Now, that can happen due to a multitude of reasons. Usually, when a Mac is frozen, on-screen activities can come to a standstill in various ways, such as a stuck cursor, clicks not generating any response, or an app window simply starts acting up or glitching in some way.
There are scenarios where even the Force Quit system won't bring any reprieve, and tricks tied to the Dock don't provide any solution either. Such Mac errors can arise due to a corrupted file, bad software update, too much load on the system resources, or simply a hardware element not working properly. On the more serious side of things, an unresponsive Mac can also be the result of a Kernel panic, which requires a fresh boot.
On a technical level, it could be due to software processes overloading the RAM, an app hogging up system processing, glitching software, or a hardware conflict. In such situations, a force restart can bring the system back to its normal state by cleaning out the temporary files and unloading the system resources towards a fresh OS-level launch. It is often the quickest and easiest way to rescue a non-responsive Mac, and also one with the lowest risk threshold.