Just reposting a reddit comment that I thought explained this pretty well --
"They keep things like this in the grey area of the rules so that they can trust the players better judgement. In other words, its like parsers while technically against the rules they turn a blind eye to those who use them responsibly and only take action when someone is using them for the exact reasons they haven't officially added them (being a dick to people in pugs about their performance)
Buying and selling houses was ok when it was done in the past because they were sold at fair prices and it was giving new players who missed the initial launch of houses a chance to own one... with this shit about people buying houses just to sell them at ridiculous prices something had to be done.
They have to keep matters like this in the grey zone because people online are dicks with absolutely no moral compass and will take advantage anything that isn't "technically" against the rules. If people could stop thinking about what they can or can't do and start thinking about what they should or shouldn't do then we wouldn't have had to have S.E. step in like this."