Good point.If the FCC changed the rules to what you recommend, I wonder how many of these AM operators would continue to try to operate their AM.Or just go dark and hold the license.
That was my immediate thought. Let's look at a real example from earlier this year ... WJLX in Jasper AL.
A few months ago, it made headlines when its tower "mysteriously" disappeared overnight. After several people in the engineering community evaluated the situation, it appears that the transmitter itself was also nowhere to be found, the building at the tower location was in disrepair, and the electric utility company had removed the meter from same some time ago.
It now appears that WJLX may have been silent as far back as the summer of 2017. But its FM translator at 101.5 remained on the air anyway, and once people started asking questions the station manager hurriedly made arrangements with iHeart to use one of their HD subchannels in the market to feed the translator (luckily for him that translator was not tied to the AM license).
There is still a question if -- after close to 2,500 days of the translator operating on its own (investigations are still in progress) -- WJLX may have both licenses revoked.
What's to stop some "enterprising" station owner to try and get away with the same thing if the rules were even looser? What Flying Dutchman proposes -- "the FM translator can be on the air as long as the licensee holds an AM license" is practically inviting abuse ... it would be WJLX, legalized.
And to answer the last part of your question, any station that does not operate for one year has its license summarily revoked, so "going silent and holding the license" is not going to be a workaround.
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Now, all that said, I do think the FCC is a little overzealous when they force a translator to go silent even when a STA (Special Temporary Authority) is granted for an AM that is off the air for technical reasons, and I would allow the translator to stay on the air for a reasonable amount of time, probably tied to the expiration date of the STA. But I would not modify the "one year or you're history" rule, nor would I allow AMs to decide on their own to operate the translator as a standalone station (unless some future FCC decision allowing those to be upgraded in status is enacted).