There are so many loop holes. I mean then they just make a company that does stock trades for them and tell that company what to trade. Or their spouse does the trades instead of them.
Spouses trading is as simple to monitor as it is for all other insider trading.
But more importantly: if there was a ban, or even a recommendation against it, and the media did its job, then being caught making peronal financial gain from your political office would make you unelectable. The strange thing about US politics is that it's not just accepted but expected. This is the cultural change that's needed.
Whether or not there are legal loopholes shouldn't matter so much. Politicians are scrutinized by media and judged by the public. Courts aren't even required.
Other non-marital transactions can be controlled - that's the basis of half the tax system in every country. The moment money leaves a household or arrives in a household, there are laws about the transaction. But within a household? All bets are off.
I don't see why the laws couldn't be like that, but I take your point.