I think you are confusing 2 different perspectives.
People not actively looking for new friends and people being resistant to making new friends.
I have moved a few times and imho most people fall into the first group. It's not that they don't want you as a friend they are just not actively looking whereas you are, so there is a bit of a inbalance in the relationship for a while where they wouldn't notice if you came or not but you would miss them if they skipped a week.
However if you keep attending the group, volunteering, or whatever you do you will see each other more, get to know each other better, start to have an impact / be considered one of the group etc. It does take time as the other people are not in a rush to make new friends.
As I said I have moved a few times. I join groups, volunteer, smile at everyone in supermarket and playground. Mostly I do this at the start because it's lonely when you move to a new town and I find it helps to fill my life with social situations. After a few months I usually find I have made lots of aquantances, we might chat after yoga or share a lift to a volunteering opportunity, chat about the weather in the playground.
Out of all those acquaintances, most will stay acquantances which is cool as it always good to have someone to pass the time of day with or share an embarrassed smile with as we run into school with dc on the last minute. But I might also make a couple of friends who I have something more in common with; maybe see a movie with that dh doesn't want to go to or grab a beer / wine after yoga to toast a birthday, or meet for a dog walk on Sat morning.
I am generally introverted and quite shy so i am not great at putting myself out there and arranging coffee mornings, nights out etc.. but I always find new friends. It just takes time, you just have to be patient, be open to whatever kind of friendship is on offer and hang in there.