One interesting, and hard, part of writing is getting interpersonal relationships just right. Romance, for example, is really, really hard to do. I'm talking real romance, not purple prose (though, without having tried it, I'm going to assume that is also hard. I just think things I have not done are hard.) Getting a friendship right is probably harder. Romance you have easy cliches to help ease you into it; that's a different whine for later though.
Friendship is harder; you have buddy cops and awkward friendships that work. But writing them well is hard. Sort of like how writing comics is hard. Ideas of friendship morph over time, as well. So, some friendships that were well-written even just a few years ago, seem awkward today. Tropes that work in some cases (you can go to TV Tropes to look through them yourself) don't work everywhere.
The other reason is that you want to show, not tell, in writing as much as possible. I am lazy; I like to handwave details whenever possible. Saying: "Jon and David knew each other for years and consider themselves friends" is easy. Crafting a whole scene where David and Jon are on the phone after their wives go to sleep talking about comic books and their kids' sports is hard. But, the second one tells you they know each other well, though not necessarily how long they know each other, unless you work in to the conversation how they loaned each other comic books when they were kids, and it is clear their friends. They're staying up late at night to talk with each other just to catch up.
The other problem is that friends act around each other in ways that often they don't bother explaining. You have in-jokes, nicknames, noodle incidents, etc., that you bring up that are never explained with real friends. Outsiders feel like outsiders. You don't want your reader to feel like an insider. He or she should be an insider. As inside as possible! You can try and weasel around this by using a point of view character or first-person narrator. They can fill in the blanks with asides or flashbacks.
Next, you have an issue with body language. When two people are friendly, you can see it. Sense it. This is why movies and plays have it easier. They can cheat and do lots of little things that if you keep describing get repetitive. Jon and David could always glance at each other and smirk at a dinner scene when either could make a dirty joke that would offend their wives or kids. It'd be funny for the audience; it would be tedious to write in every time they do it, and if they only do it once it doesn't show us how much they are on the same wavelength. But, with a visual medium, you suddenly can cheat! You can pack more information in less. Cheating like this is good!
So, writing friendships is hard. By the end of this blog's run, you can probably make a list of things I whined about being hard to write.
This is a mini-theme at Althouse's blog. She linked over to this NYT piece, that says: "Schedules compress, priorities change and people often become pickier in what they want in their friends."
You can start the process of turning random people in random places into friends just by talking. Also, it helps for people to be as judgmental as they were in college as opposed to as uptight and narrow-minded as the NYT thinks we become as we age. In college and high school, people my age routinely had friends with radically different beliefs than theirs. If that's not still happening once you get older, ask why.
The NYT is trying to make things harder than they really are. Also? Several of their examples of friends not working out are just people being jerks. Who asks about other people how much they make, and who does not know the proper response is: "Enough?"