The rule you're annoyed about only have good intentions for the roleplay itself. Now whether or not it should be considered a standard and if everyone will like it, is all up for discussion, and I'm not certain I'd have such a rule myself on any roleplay hosted.
But the thing is, having a criteria or rules such as "Avoid having 3 or more roleplays including this one" or just "Don't have too many roleplays" is really all about devotion towards said group. I know some people have more time than others, but in all honesty, if you have 5, 10 or 20 other groups, you will not be paying enough attention towards the ONE said group. It's arguable how much attention a person get time to spend on particular groups or how many balls they can have up in the air at once, but you will simply not give the group or provide the group what the roleplay hoster wants if you spend time in loads other roleplays. One good roleplay can easily take up all of a users time without them needing to roleplay hop.
Hence why the rule is there, even though I never used this myself, or see it that often when I check around, it does make great sense to me.
In my roleplay I wouldn't want to have people that constantly went into other roleplays when I myself or others sit and try to make something special while others just slide on a banana peel or only join when the fun action starts, and never do anything to get there. Everyone wants to host and have the go to roleplay, and many roleplays probably need time to grow with it's users, it doesn't happen over a night, and that's where you or any user come in, to help it become something. A roleplay is nothing with the hoster alone.
So overall, it's not that much about which roleplay you are in, or what you do there, or why you're there, it's more about making sure you are willing to dedicate yourself to the ones looking for people to their roleplay. About reliability.
It helps to think from both perspectives in a matter like this. Don't get me wrong though, I can understand the question can get annoying or shouldn't really matter too much, but I believe what's written above have a lot to do with why the question is there.
