Most people are self-absorbed; it just is what it is. Relationships wax and wane -if you don't want to help, don't help. If you do, then do. When our self-interests collide and overlap - ah, that can be the beginning of a beautiful friendship.
Friendships develop from good conversations, shared interests and shared experiences. Frequently, friendships begin because one person needs something from someone else; that's pretty natural. But there are boundaries that need to be set regarding what's expected out of those relationships.
I like it when people ask me to help them; often it means that they respect me and my opinion enough to request it, and I appreciate that. Sometimes, however, they can act like succubi - just before they wrap their vacuum-cupped tentacles around you and smother you in the fuzzle that is their lives, preventing you from being able to breathe let alone get angry and burnt out on their drama, you need to tell them - oh, sorry, I'm busy.
It doesn't happen that often to me, because, frankly, I am a lonely pathetic person who needs positive reinforcement to my fragile and wussy old ego all the time, and so will do pretty much anything that someone - especially someone that I consider a friend - asks me to, if it's all possible for me to try to do and so long as it doesn't involve some kind of compromise to my integrity. I will try to do what I can, sometimes even if they don't ask.
Except, occasionally, call them back, until, whoops, it's too late to get to that favor they'd requested. Passive-aggressive you say? Who, moi? Nay, just oh so busy!
• My approach would be very much like your own. I am always prepared to help anyone, and certainly don't do something because of what I may get 'in return' but there does need to be some element of reciprocity.
I think there are two kinds of people, those who give and take and those who just want to take.
I think the following quote sums up, for me, what friendship means:-
"I value the friend who for me finds time on his calendar, but I cherish the friend who for me does not consult his calendar." Robert Brault
And as Marlene Dietrich put it:-
"It's the friends you can call up at 4a.m. that matter."
• "It sounds like these people are not so much friends as opportunistic acquaintances."