Why aren't cascaded NOT gates used as frequently as flipflops?
Because connecting 2 outputs together is bad in the general case. your schematic requires that the input signal overrides the output signal in some way, but not all the time (to be able to use it as a latch). This means you can't use binary signals to control this latch. You need a third input state that says to output whatever is latched.

Look up how a SR latch is constructed, a non-gated SR latch is exactly 2 gates. 

However you rarely need the pure SR latch. Most of the time you need the latch to be clocked (latch on clock edge) or be gated with an enable input. That requires extra logic.