Face Chasing and User Chasing?

What makes people go after a specific character or user  in roleplays? I understand that if another character is from the same group or company or they have actually met and have some type of connection it's a lot easier to talk to them and roleplay. What I don't understand is why that often entails only wanting to talk to or be around them and acting as if other people don't exist. I know most people have favorites and characters they really like and prefer over others. But limiting yourself to the same faces, doesn’t that get dull and boring after a while?  Isn’t the entire purpose of joining a public roleplay to talk to and interact with other people? If a character I happen to really like or has some connection to mine ends up being in a roleplay, yeah I'll talk to them, but I don't sit and chase after or only talk to them. The same thing goes for people who are clearly friends or have history together and make it very known. Again, I get that the familiarity makes it easier to to approach and interact with certain people, but why does it usually end up meaning you exclude or hardly pay attention to other people? What exactly is the point of being in a public roleplay if you only intend on interacting with specific characters and friends or acquaintances? I know some people probably don't realize that they're doing it, but a lot of people also make it very obvious that they intend on chasing after and interacting with someone specific. I'm just really curious about what makes people do this in public places instead of just making a private roleplay for their friends or pm roleplaying if they want to roleplay a certain couple or as certain characters.