I think the places where the friendships are the hardest all tend to be guess cultures[0]. That isn't exactly surprising to me. Guess culture should make creating friendships much harder. If you may only ask if someone wants to hangout until you are very sure they'll say yes, then you'll very rarely ask for that. You'd need circumstances with long periods of being 'stuck' together to make a friend. Thus you'd expect people to disproportionately from work or school.
As someone who believes in the Moral Foundations Theory, I don't think it's an accident that the places that are known for low friendships tend to be culturally liberal places. Since most probably don't know what Moral Foundations Theory is, a quick and dirty version is that all moral judgement can be reduced to the following core values (or moral foundations) which I copied from Wikipedia:
* Care: cherishing and protecting others; opposite of harm
* Fairness or proportionality: rendering justice according to shared rules; opposite of cheating
* Loyalty or ingroup: standing with your group, family, nation; opposite of betrayal
* Authority or respect: submitting to tradition and legitimate authority; opposite of subversion
* Sanctity or purity: abhorrence for disgusting things, foods, actions; opposite of degradation
I'm also a fan of the tentatively accepted liberty vs oppression foundation. I really think it should be renamed to something like agency vs domination. Anyways, it would value being able to make decision on choices deemed important and rejecting those who coerce others.
Anyways, culturally liberal places pick care vs harm as their primary value and in some cases have made it the default choice for answering moral issues. I think this naturally leads to guess culture. You get told as a child, frequently, that saying "no" can hurt the askers feelings. You learn to feel bad for saying "no", since it violates care vs harm. You realize that the person you are about to ask a question to is going to feel bad if they say "no". Making them feel bad would be harm, so asking would be harm... unless you can figure out if they'd say yes. That's how I think a guess culture would develop.
The reason I bring up moral foundations at all is I believe the solution is in the last 3 foundations: loyalty, authority, and purity. Those 3 are characterized as the group-ish ones. They are what separate acquaintances from friends, neighbourhoods from communities, and coworkers from a team.
[0] - https://www.theatlantic.com/national/archive/2010/05/askers-...