Having many shallow relationships is the first (well, second) step towards having a few deeper ones. You can't befriend people you never meet, and people find it extremely offputting for someone they don't know to immediately try to be their best friend.
Plenty of my former coworkers have evolved into lifelong substantial friendships.
What started with smalltalk evolved into conversations over lunch which then afforded after work socializing which then led to actively scheduling time for shared interests. All of those provided ample opportunity to learn almost everything about that person and open the door to a deep friendship when mutually desired.
Have you never made a deep friendship? How else would anybody make deep friendships? First you do things that let you meet people, then you make acquaintances, then you make setting-specific friends (work friends, gym buddies, etc), then you start inviting/being invited to do things that aren't based around that shared setting, and then you have friendships.
Either that or your definition of deep friendship is substantially off.
Most of my deep friendships were through friends and family. A handful at work/school. And it is the same way for most people I know. But I'm not American, so that's that.
Making friends through work and school are pretty much exactly what I described. You go to a place with people, you meet a lot of people, and some of the shallow acquaintances end up becoming long term friends.
It can be any other activity that requires more than one person. For example I started going to dance classes with my partner in november and what was just awkward "hello there" interactions before the holidays when we had to swap dance partners is now a bit more comfortable and we exchange a bit much and even have a chit chat after class at the door. It is waaaaaay too early to know if it will create new long term friends but the dynamic is here and after just a few weeks I can already spot the people I have absolutely no wish to know more about and those that I feel natural chatting with.
