Civilian drones are fairly new. There are century old GA aircraft still flying around. I'm sure the FAA would love to require them all to carry radios and transponders but it's technically and politically difficult to impose new requirements on old certified aircraft. Some owners can barely afford to fly as it is so they'll resist any new mandates.
This is a common argument but makes little sense because the accident and loss rates of GA is so incredibly high. The cost of an ADS-B receiver for example is only $200. Full transceivers are a few thousand.
Aircraft owners are already paying well over that as insurance rates yearly because of all the accidents, so total cost to fly would likely decrease by mandating things that actually move the needle on safety, especially ADS-B and fuel alerts.
