Because the article is very misleading.
Smartphones MAY have a chip in them that is capable of receiving FM transmissions [probably as part of the Qualcomm/whomever chip for processing cell phone signals].
But not a matter of 'just turn it on' and everything magically works.
You need an antennae/other external hardware that receives those signals properly. I'm not an antennae engineer, but you either need a separate antennae [which would totally be a non-starter] or you have to compromise the design of existing antennae, because now it has to work for more frequencies.
You also need the software side to work. Since the signal is [most likely] coming from the cellular chip, it also affects the separate baseband software, as well as the main OS.
Then they need to see how it affects battery life with an additional radio turned on, as well as how it affects cellular, wifi and bluetooth reception/transmission.
And don't forget that NONE of the wireless carriers in the US would want the phone to have this feature, because it means the user can be listening to music that they are streaming to their phone FOR FREE, and the carrier would be making no money from it at all. They would rather the user just have the choice of 'do without or preload the music on the phone or pay for streaming music on the phone by paying the carrier extra money] (and they would really prefer to prevent that middle option, but that would have been a really tough sell earlier and impossible now].
Finally, these whiners wouldn't stop at just 'enable the FM reception' capability. It would be 'automatically detect an emergency broadcast and switch to FM automatically when one is broadcast'. Which means another radio always be on. And if that happened...how many days before an FM station sent a fake signal that would trigger this feature without really sounding like an emergency broadcast signal, so the phone would automatically switch to their station for a few minutes. And they could just say it was a bug in the cell phone, that they didn't broadcast a full, real emergency signal.
Anyway, Apple never did this, because they want people to get their music from the iTunes music store, and everyone else doesn't because the carriers won't let them [at least here in the US].