It's not necessarily you it's probably them. It's easy to stick with the familiar, the tried and tested. It takes a bit of effort to remember to include the newbie, to add their name to a list.
If asked they might say oh yes, wheredoistartmrs, she's really nice! But they have their own set of pals you don't quite fit into. They have you mentally listed as DD's mum, the one who wears this or does that, one of the crowd. You aren't doing anything wrong, they just have time allocated to this or that alternative person.
Join stuff, get known, try neighbours, school, sport, community things, charity/fund-raising, church?
I moved house in the summer and whilst I can say I have new acquaintances I wouldn't classify any of them as friends (yet). You will 'click' with someone. In a way it's like dating. You can get off on the right foot, all seems to be going well, but sometimes things peter out. Nobody has actually said to me yet, "I have enough friends thanks, I don't need you" but yes a couple of times I have felt mildly rebuffed. I can shrug it off but now my DCs are grown I don't have school as a short-cut to meeting people so have to put more effort in.
Finally, have you peeked at your Local area on MN for events and meet-ups etc?