Why does a MOSFET have 2 semiconductor leads?

I have a question on the mosfet construction. Considering a n-channel enhancement type mosfet, it has two n-type regions connected to source and drain terminals. Also there is a p-type substrate. If source is connected -ve and drain is connected +ve voltage, there is no current flow unless there is a positive voltage in the gate which attracts some electrons to form the n-channel and hence conduction occurs.

It seems the same effect could be achieved using only one n type region connected to drain and no n-type region connected to source in the mosfet. alternate mosfet implementation

There would be an depletion region with p-n reverse biased (drain +ve and source -ve). Gate being in a positive voltage can create a n-channel and let current flow. The device could operate in pinch-off or linear or saturation region.

I was getting the feeling the source side n-region is redundant. Would like to know if it serves a purpose?