I think it's a symptom of American mentality that atheism and deep meaning are considered opposites.

I don't think you're wrong to analyse your friends, I think you're right that Americans pivot toward religion (or the ill defined "spirituality") when they feel they lack that something else.

But in many other places, including where I live, it's natural to lean on philosophy, personal connections, family, teaching, social work or any other "deep fulfillment activities", and in fact the kind of empty success you describe is frowned upon, among atheists just as much as among religious people.

Philosophy is part of the basic school curriculum from secondary school, and dealing with the big questions is not left for mass.