I've wondered about this a lot. I don't think our generation (I'm assuming most of us are millenials) operates in this regard in the way even our parents did and other than the prevalence of social media and possibly because of more diverse demographics, I can't really understand why that is.
Why do we suddenly get very inward-looking in our 30s when it comes to forming new friendships, especially among the more affluent?
So when you are in your 30s, you have limited time and limited opportunities to make friends. If you don't spend a lot of time hanging out with someone it is tough to make really good connections. Other factors come into play as well - comparing yourself to others, more niche interests, lack of desire to invest time, having a partner, etc.
This is typically the time when you or those in your age cohort are focusing on their families. Time is at a premium.
What I find hard to tolerate are long-term toxic relationships that will require enormous effort and a long time to correct. I have enough of my own to deal with, I don't want to be drawn into yours, especially if you're unwilling to listen or take positive action to change.
So for me, at least, getting older means I'm more likely to avoid getting to know you if friendship with you comes with hearing about a lot of pre-existing drama that you are willing to tolerate, or perhaps even instigate. If you want help, I'll help, but I'm not out to save the world, and I don't need any mayhem in my life.