Only ask if you’re prepared for the answer.
It’s very easy for people to sit here and say that the group are obviously all bitches and you are clearly best off without them, but the reality is that none of us know them and none of us know you, so it’s not possible to know why this has happened. It is entirely possible that they are cliquey and that you don’t fit into their clique, in which case you’re better off without them. But it’s also possible that there is a legitimate reason why they feel they just no longer want you to be part of their social group. And it may not even have been a conscious thing in the beginning, there may never have been an actual conversation about excluding you, but if you’ve done something or have some trait which they find difficult then it stands to reason that they just may not identify with you on a group level any more.
Im sure that there are people here who have been excluded and have no idea why. But equally I’m sure there are people who have been part of a social group where one person or couple is such that they don’t want them on their evenings out any more for some valid reason. And their not telling you might actually be to spare your feelings, because actually it’s not that easy to tell someone you find them offensive or difficult etc.
There used to be a school mum at my DC’s school who found it difficult to make friends. People befriended her, in fact I was friends with her on an individual level and we still have some contact. But people started to invite her to social events, and once they did it very quickly became clear that in a social setting she would become drunk very quickly and hysterically upset and start becoming very over emotional about her life. The first couple of times it was something which people sympathised with on the basis she obviously didn’t get out much. But this became so much of a habit with her that it would bring the whole tone of the evening down, and someone would invariably have to drive her home when she became too drunk to stand. The result was that people just stopped inviting her to group social events, but no-one would have had the heart to tel her because individually and outside of the group social setting they got on, but put her into a group and it was a disaster.
Not saying that you’re like this OP, but there is genuinely no way of knowing that there isn’t an issue here, so if you really want to know, ask yourself first how you will feel if they come back with a legitimate reason why you’re no longer invited to events. Otherwise just accept that this isn’t meant to be and move on.