And you were the one telling me to go and knock on the door of someone I haven't seen in years! I daren't even contact her online, though I'm convinced I'd get a positive response.
It would be nice if friendships and acquaintances could just start again from where they were left, and the very least, it would be nice if previous interaction was acknowledged rather than shrugged off or ignored. But I can certainly appreciate from my own experience that other people might feel unable to invest a high amount of energy in a brief encounter - it might be too upsetting to the psyche or it may mean the individual fears 'wasting' time with trivial banter which may lead onto many awkward activities and then finally not seeing each other for another fifteen years.
I think perhaps some people may well consider their friends to be everyone who is agreeable in their surrounding environment - if someone pops out for five years and then comes back, they might as well be a stranger.