In our post for WCAG 2.1.1, we discussed why it's important for your site to be keyboard accessible.
In a nutshell, some experiencing visual or physical limitations rely on keyboards and keyboard emulators to navigate the Internet. Wherever possible, your site's functionality should not require users to hold down a key for an extended period of time or to hit a certain combination of keys within a short period of time.
Whereas WCAG 2.1.1 outlined the Level A standard for keyboard accessibility, this
You might recall from our post for WCAG 2.1.1 that WCAG allowed exceptions for interfaces requiring "path dependent input", like free-hand drawing programs, or even flight simulators, where their functionality was necessarily dependent on the specific timing of the cursor's movement or on making an inordinate amount of keystrokes. WCAG 2.1.3, in contrast, does not allow for these exceptions.
Please note, the expectation here isn't for you to make such functionality keyboard accessible. Rather, if you wish for your site to meet the higher standard this guideline describes, then you need to avoid these components altogether.