I agree with your perspective - at least to a large degree. Our style is also much like that (no rules-no limitations). But I also understand and tend to be maybe more empathetic with others and their particular situations. I think it's important to remember that most people are in their infancy in exploring what they see as having potential for something good. And yet I suspect we all know the horror stories that abound. If you've ever had open discussions around poly loving in a mixed group of poly minded and mono minded people you soon learn the fears and misinformation that circulates. I also respect the fact that relationships are (as others have mentioned) more than just an emotional one. There can be various physical factors involved (kids, finances, property etc) that really have to take priority for the greater good. You've shown your understanding & respect for that also.
But maybe here's another angle to consider...........
When we come across situations like this we try to dig beyond the "rules" by getting to know the individuals more intimately to understand why those rules may exist. Rather than blow them off because they don't meet "our" immediate need or perfect world view, we sometimes ask what "we" can contribute to them to help them move forward with their hopes & dreams. By giving them the opportunity to proceed slowly into waters that they want to swim but are afraid because of all the negativity commonly associated, we're trying to add to the net-positive. Rules can and often DO change because they are often constructed to protect against worst case scenarios. We all know even the nicest, best intentioned situations can turn ugly - sometimes because of factors not really related to the potential poly situation.
It's wonderful that you've stumbled upon some folks that are more evolved in their practice. We'd all wish for that. But in the mean time we also feel we have a valuable role as teachers - givers rather than receivers.