A bigger issue than the available of updates is whether security updates are automatic and mandatory, or optional for the user. If a security update requires some action on the user's part, most users won't want it.
The overall problem is that the main IoT security problem is botnets, not insecure devices per se. A botnet does not affect the owner of a device very much. Thus, the owner of a device usually prefers an insecure device, rather than taking some risk of the security update breaking the device.
I'm not sure what the FCC should do here. It seems reasonable to hold the manufacturers of devices responsible in some way when those devices are used in a botnet, but I'm not sure if that's within the FCC's scope.