Most chipsets have the FM receiver. Most do not bother to hook up the antenna. As it would be one more thing for them to support and test.

Didn't they all require wired headphones to function? That's probably why it got dropped.

It is just a pin off the chipset. The headphones was just a cheap way to get a 'free' antenna. Those chipsets do a lot of stuff. If you printed out the docs it would probably be a couple of reams of paper. They fuse things out for different cost points and just do not hook things up for others. It can also be if they hook it up it is an extra dollar per device. Not saying that is what happens but it is a distinct possibility considering the way they bifurcate the cost of those chipsets. From a consumer PoV though it is frustrating as the HW is there...