Because they are increasingly outnumbered by younger people. The social norm changes, probably faster than they're comfortable with, but with or without them as they die out. Black people go from slaves to sharecroppers in a generation, but it takes over a century for any of them to become millionaires, CEO's, and presidents. Women have progressed even slower.

My grandparents are all dead, but I suspect that few of them would be pleased with the prospect of a black president. Even my parents would be less than pleased to learn that I was bisexual.

Your grandparents may be more open minded than mine, and that is a credit to them. But for every one of them there's ten old people who don't keep up as well.