Well put Plucked. I think you are right and that in the end, it boils down to being willing to put yourself out a bit for your friends......and yes, being a good guest with generous gifts etc doesn't compare with hosting.
It's perfectly possible in a small, untidy flat, even with little money, to invite someone or two people for coffee and a cake.
Isn't this partly about recognising that those who have often hosted you, might also enjoy an invite themselves sometime too. You don't need to become the party thrower of the year to be willing to sometimes go out of your comfort zone just a little bit, because you acknowledge the rightness of giving those who have frequently hosted you the chance to be the guest for once.
And yes, I agree that reciprocity can take a variety of forms - you might invite those people instead out for a meal or a drink in the pub or a coffee, or to the park for a picnic.......but to never offer them any kind of invitation of any type, having received their hospitality on numerous occasions just strikes me as very socially unaware and to be honest, quite selfish, u less it's to do with health issues.
Not all people are natural hosts and party givers. Like lots of things, we sometimes need to push ourselves a bit with things we find hard. We can decide that because our flat is small or cluttered, or we are not confident cooks or confident hosts that somehow we are justified in never inviting people to anything at all. I agree that these things can exclude you justifiably from throwing a big party - but these things don't exclude you from inviting those who have often invited you for a coffee or if you really cannot push yourself to allow anyone into your home, for a drink in a park or pub or park.
Hearing from all the hosts on here, it's so obvious that lots would just really appreciate an invitation to something - it really doesn't matter what. They don't host to receive return invites and most aren't keeping a tally of invites they receive to those given, but when they invite someone time after time and never receive so much as an invitation for a coffee, no wonder they feel the relationship is really skewed.....and at that point I think that people are actually taking the piss and need to stop making excuses and get on and recognise that relationships are a mutual thing, where both parties have to make an effort. Otherwise, they really are starting to look like sponges. Perhaps they are, with no real interest in the hosts at all, just in seeing the other people there and enjoying the hospitality given. It certainly starts to look like this is over a long period of time, they always receive hospitality but never make any kind of offer or invitation in return.