system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do most smartphones not have built-in FM receivers? (When they have many other technologies like WiFi, GPS, 4G, etc.)
gpt
This is probably for a number of reasons.  For one, people care less about FM radio than before.  Second, device manufacturers might have a profit motive in selling audio content and other sources of media rather than FM radio.

There are some unique complications with FM, though, compared to the other radio technologies in phones.  It is on a fairly low frequency, so an effective antenna needs to be relatively large.  It is also an analog technology that can be a little bit more complicated to design in than digital communications standards.

It is very challenging to design many radios close to each other.  Mobile phones already typically have, at the very least, a couple of bands of radio for the cellular technology; BlueTooth; and GPS.  Many others add near-field communication and WiFi.  As you add radios, the chances that some of the radios interfere with or hamper the performance of others increases.  This is not insurmountable, but it's already very impressive the number of radios that are put into such a small footprint.