Speaking honestly here I have a few friends from school all but one of which I will see maybe only once or twice a year, I have probably only one friend from that group that I still see on a regular basis. The thing is though that suits me just fine, I have my kids girlfriend and family and they keep me busy enough, I rely on my friend for lifts to work occasionally when I have to drop the young one off at school, he'll tap me for some cash until payday, we schooled together, shared a room at Uni together, we're each others kids Godfathers, you know life long friends, the sort of thing that’s hard to cultivate from scratch once you're in adulthood.
I'm at an age now where I don't feel the need to forge new lasting friendships of that sort of depth. I know plenty of acquaintances and occasionally I'll go on a works night out for instance and if I'm down the pub I'll see plenty of people I will stop to say hello to but I wouldn't think to contact them out of the blue and ask them if they fancy a social drink or to talk about something that’s on my mind. Of course when I'm out I'll listen to people talk about their lives and have a deep an meaningful if needs be but its different from my friend who I can go to with my latest crisis or vice versa.
So I think that’s the problem for a lot of people trying to make new lasting friendships that go past being acquaintances, people are just reluctant to look for that level of friendship and commitment to someone as they have their lives to lead. It’s the same as being single really (albeit as a friend it’s ok to see other people!). I could make new 'close' friends but I would still choose to call my closest friend for the odd social night out that I manage these days. So I guess it is hard for people when they don't have that, people generally prefer to play the field regards any friendships beyond the life long friendships they have already made, you in fact probably need to find someone who is in a similar boat; "platonically single" and has the desire, time and capacity to allow a deep friendship to develop. I think it’s easier to find a romantic partner than it is to find a platonic one, as with a romantic one commitment generally comes as being assumed and part of the deal.