Windows 3.11 was nothing more than a very advanced Dos Shell. Like it's precursor DOSSHELL or GEM. Though, that did slightly skew with things like WinG or 32s that made it more shaped like a proper operating system.

To explain simply: Windows back before the NT Kernel, could not exist without DOS to use as a foundation.

And in fact, this was how it was until Windows ME. Of course, exiting to DOS was discontinued after Windows 95.