macos – Why does clamshell mode work that method?

To make use of a Mac with the lid shut, i.e. Clamshell mode, one wants:

1. An influence adapter
2. Exterior Mouse or keyboard
3. Exterior monitor

Now, why is that? I imply why did Apple design it that method. I am certain there wants be a rationale.

I do know one can use third-party apps or terminal command, together with the undocumented (no point out of it in man pmset) pmset disablesleep 1.

However that is not my query. I need to know the rationale behind it, or not less than doable causes for it.