Max con - but if no-one is listening on 121.5 in class G airspace wihout an ATC service, how will they know that a TRA has been setup?
MD600 - if you listen to 121.5 you will hear airline crews inadvertantly transmitting on it all the time but we don't launch for them so why should we for a stuck PTT. If you call for help on 121.5 in an EMERGENCY you hope someone is listening - if everyone monitored 121.5 then you would have a greatly increased chance of being heard.
Since most aircraft cost a lot more than a boat and an engine failure or other malfunction is usually more serious in an aircraft than a boat, the extra cost of the radio is probably worth it - unless you subscribe to the big sky/it'll never happen to me theory. No-one goes out with the intention of having a RTA but they still occur every day.
SS - you are not quite correct - the SARSAT/COSPAS satellite system will stop monitoring 243 and 121.5 because of many false alarms (beacon hits) and the fact that 406 beacons are becoming more prevalent and are a. registered and b. able to send a GPS position as part of the distress message. 121.5 will still be the VHF emergency freq should anyone be bothered to use it and most 406 beacons will have a 121.5 capability built in.
If all aircraft had 121.5 monitoring then the laxative bath salts would be much more likely to produce results even in the low level or geographically unsuitable environments.
Maybe ATC should stop monitoring 121.5 since it clearly is of no use.