I haven’t rtft but I think people having kids is a massive reason for this. I disagree with pp that it doesn’t make any difference to true friends.
Life is so much more complex and demanding now, especially for working mothers. Generally speaking, men are not picking up enough slack.
In the past, sending a child off to primary school involved putting their gym plimsolls and lunch box in a drawstring bag. Now parents are involved in reading, hwk, projects, extra curriculur activities, fund-raising, fancy dress, parents evenings, concerts, it’s exhausting. And children get ill. Working parents travel.
The intensity carries on throughout a child’s secondary and tertiary education.
Nearly every family commitment is more complicated too; look what a bun fest Christmas has turned in to!
I do loads more for my teen and adult dc than my parents ever did for me! And many of my friends are doing regular childcare for grandchildren. Life gets more and more demanding.
However op, I have found a surge in friendships now my friends are late fifties early sixties and women are reducing hours, retiring or their dc have flown the nest permanently after a couple of false starts.
Op my advice would be to rationalise your organising and pick an interest of yours. Set up a club around that interest. Make it weekly or fortnightly but keep it low cost and casual and make it clear no pressure If you can’t turn up one time; so you have built in “flake” weeks.
Then meet in a local pub or restaurant; premises will often let you use a place free of charge on a Mon or Tues night if it brings in drinks custom. And yes you will have to put work in with admin and buying materials or arranging walks or whatever but you will have everyone’s name, and email address and it’s a brilliant way to meet people, Keep it bright and breezy and let friendships develop naturally over time. Good luck.