I had a friend who invited spouses, but on the RSVP card had a box for which spouse were coming – or both. Honestly, it’s a waste of money to book a seat for a spouse who isn’t coming. And it’s not bekovodik to not invite a wife.
That said, if this was a more simple affair, or the families are tight on funds, this would be pretty understandable. I had a chavrusa who had a family tragedy a couple of months before his wedding – and I never got the invite. This was over ben hazmanim, and I haven’t heard. I nearly called him to ask if everything was OK, when a mutual friend told me what happened. They ended up have 10 friends each at the wedding, doing it in a local restaurant. I can’t say it’s insulting that he didn’t think to call me. I’m just happy he was able to pull through and get married.