There's no evidence of a Maine lobster trap ever killing a whale, and the most recent evidence of one injuring a whale is more than a decade ago. Canadian (and for that matter other states with weaker regulations on traps) traps on the other hand there is plenty of evidence of injured and dead whales. You're right of course, you can't prove a negative, but when there isn't evidence of Maine lobster traps harming whales but there is evidence of other states and countries traps doing it, the solution isn't to assume Maine is just as bad as the others and getting lucky, but to look at what Maine is doing that they aren't.

Maine has far stronger whale safety regulations than other states and especially fucking Canada, which are widely if not universally observed, because even if lobstermen don't give a shit about whales, they want the industry to be sustainable.