You are correct about the much larger weights and masses being pulled with cars and trucks, but look at them as a percentage or ratio of weight pulled vs. weight of vehicle pulling it.
I've been looking at the various makes of motorcycle trailers, and some of them weigh as much as 250 lbs. and that's empty! I'm guessing there will be plenty of riders who will load their trailers to the max and so now your talking anywhere from 400 to 500 plus lbs. Now look at the weight ratios of these against the bike. The K1200lt comes in around 840 lbs wet, empty, and not counting the hitch. So, the ratios become comparable.
I said I agree and prefer a trailer breaking away in the event I end up laying down my bike. Don't need a loaded trailer compounding the problem and possibly winding up on top of me.
So, that being said, the one chain on a motorcycle trailer is useless, unless you're going to use it with a padlock to keep someone from stealing it while it's parked.
Even if you don't lay down the bike, if the trailer decouples, the tongue's going to hit the pavement, drag, maybe try to dig in like a boat anchor, and depending on the strength of your "safety chain", it'll quite possibly cause you to lay down the bike.
BTW, I've seen some of these trailers with electric brake options, so the weight must be a concern to some.
Common sense should rule here folks.