They took it away because they felt sponsors could abuse their spouses by threatening to deport them if they didn't do whatever they wanted. Honestly it's a stupid move to remove it. If the spouses were abused, they could just report to immigration and they would be allowed to stay. If the spouses were in a legitimate relationship, living together for 2 years is a more than reasonable requirement, and the condition 51 would do absolutely nothing.
Even if the sponsor wasn't really abusing, and was just hinting at possible deportation, there's no reason for the spouse to continue to live in that kind of relationship, and just simply divorce and return to their home country. If I ever threatened to deport my wife if she didn't do what I wanted, she would've just simply said, "OK fine", and buy a one way ticket back home the next day.