Because it's the right attitude. She's old and lived a long time and has a lot more life experience. Respect is even scriptural.
This story leaves out a lot of info. Do you know if Mom & Dad are disrespectful punks like the kid? Would you want some younger person disrespecting your Mom or Grandma?
Too many people have forgotten what manners are.
I know a lot of nasty old people and they are not going to get respect from me just because they are older. That is completely ridiculous. Just as this woman in the article is just a nasty human being.
On the other hand, I know a lot of wonderful old people as well.