While flaps do slightly reduce stall speed, that is not their primary purpose. Planes pass quickly through both Vs0 and Vs1 during takeoff or landing, and pilots are too busy to mess with flap settings during those few seconds anyway. The only reason we deliberately fly inside that range is to practice slow flight, stalls and spins, where such an interlock wouldn't be of any benefit.
During takeoff, low flaps may be used to increase lift and thereby shorten the takeoff distance on short runways or get into ground effect sooner on soft runways. In both cases, though, the climb afterward will be slower due to the added drag, so it's only done when necessary and then pulled out at best climb speed, i.e. well above stall speed.
During landing, high flaps are used to increase drag and thereby descend without gaining speed. You're not even close to stall speed until the flare, and raising flaps before then just means you'd land faster--not stall.
OTOH, while the benefit (if any) would be tiny, there is a very real risk that the device would fail somehow, such as preventing flaps from retracting at any speed, which is a serious safety problem. You would need a way to bypass it in such cases, and if you trust the pilot not to stupidly bypass it, then you might as well trust him/her not to stupidly need it in the first place.