IMO cancelling plans on people because 'something better came up' is rude and selfish. I just stop being friends with people like that.

e.g. I had someone cancel plans made weeks ahead to meet up with me and my family at the last minute because they got invited to go skiing (this is in an area near many ski resorts, it was not a once in a lifetime opportunity). I just lost interest in meeting up with that person again.

I similarly dislike dealing with people who "keep their options open" by refusing to commit to plans until the last minute (e.g. RSVP-ing to a birthday party invite the night before).