Yes, it may very well be a way to distance themselves but to say there is "no reason not to return someone's call . . . within a reasonable amount of time" assumes you know everything going on in that person's life. It may be absolutely true that you are not a priority in that person's life right now, but what you don't know for any certainty is what might actually be a priority in their life that has taken precedence over making that phone call. Yes, it may be nothing but avoiding you, it may just be laziness, but on the other hand, there just might be a reason that you just don't know about and that they aren't ready or willing to share with you or perhaps anyone at this time. Sometimes people just outgrow certain relationships, change their focus, etc. and don't know how to diplomatically communicate that, so "busy" is their poor way of communicating that they have moved on. Not fair. Not right. But it is what it is.

What some of us are saying is that rather than assume they are simply being rude, perhaps consider that there might be something going on with them. It doesn't mean you have to continue to try to interact with them. It doesn't mean you have to remain friends with them. It doesn't mean you have to like it or condone it. You can proceed however you wish. But to not take any consideration that, like it or not, they have their reasons for not communicating with you, leaves out the factor that, like you, they are individuals living their own life, with their own struggles and challenges. It isn't good form, but sometimes it is about more than just finding the time.

If you are having trouble with particular people not reciprocating in a relationship despite your best efforts, then you do what you need to do to move on and seek out better relationships. Hope it works out better for you in the future.