Leaving the Wedding - I can think of a half dozen reasons that a person might only go to the wedding. Most have to do with being a caretaker for someone. Usually the person would have just declined but the couple is important to them so the guest goes to the wedding because that is the important part.
I've also attended weddings where for religious reason people did not attend the wedding ceremony, but did go to the reception. My Uncle's 2 daughters, were raised by their Mother in a religion that forbid them to enter another religion's sanctuary. When he married, they came to the reception only.
Weather announcements on air planes. How about because that is how we have always done it? When we started long distance flights people didn't have an app on their phone that told them the rain at their location will start in 30 min and stop in 1.5 hours. (dark sky used it today with the kids). Not that it would have done them much good - their phone was hard wired into the their house. I can remember leaving Houston to go to PEI. We knew the general weather Mom grew up there and we were frequent vistors - but after traveling for for 18 - 20 hours (including layovers) we had no way it know if it was clear or raining. Being an island in the gulf stream that can change quickly, and on PEI you walk across the tarmac to the terminal. (We had umbrellas in our carry-ons just in case.)