It does appear to be quite rude seeing that you introduced them, but they may have had some kind of reason.
If you are in the position that you can do this, I would try to invite all 3 couples around - maybe for 2 or 3 of your monthly meeting to start of with. I would hope that if you lead by example that everyone can come along, than maybe they will invite everyone too. If it's too large a group to accommodate in your house, just meet up in a restaurant or cafe. Trying to be more inclusive to all.
Hope you can have a friendship with all the couples. It sounds like you all had fun before Covid, try not to loose that.