AIBU School Play do other grandparents get invited?

Son and girlfriend have 2 children age 10 and 6. This year I started thinking that we never get invited to the school nativity play for either DGC. We also don't get invited to any birthday parties either just told we can call in for coffee and cake in the evening or the next day. Son brings the children to see us every 2 or 3 weeks sometimes DIL comes with them. My MIL was invited to all birthday parties and school plays etc even though I disliked her. What do others think. I usually learn if they are ill, going for a day trip, or in the Nativity Play from Facebook which is not really very good.