He’s just sticking to how he grew up hearing it probably. Maybe he thinks other people pronounce it incorrectly. Why do some Black people say aks instead of ask when 99% of the people on TV and probably 99% of the white, Hispanic, and Asian people around them say ask? They most likely know how to spell it if they are literate.
Remember how Hillary Clinton was criticized for altering her accent and pronunciation when she was in the Midwest, South, and Northeast. That’s actually normal. Usually, people conform to the region to some extent. She spent many years in all three.
Pronouncing something very differently from how it’s spelled can be because the person doesn’t know how it’s spelled, which was mentioned above, or just their dialect. Or, if English is their second language certain sounds are very hard to say as an adult. Like my inlaws can’t pronounce TH well.
My husband can’t pronounce sill. I don’t get it. He can say will, thrill, bill, but not sill.
A woman I knew in Tennessee named Jenny one day was asking me if I had a pin. Eventually, I realized she meant pen. She admitted she knew that some people say pen. I asked her, “so do you pronounce your name Jinny, I’ve been calling you Jenny?” I asked because I simply wanted to pronounce her name as she preferred. She said, “no, I spell it J E N N Y.” So, I asked, “then why do you say pin for pen?” It just seemed so inconsistent to me. She smiled and realized how inconsistent it was.
Just a week ago a friend of mine wrote a pet peeve of hers is people mispronouncing mischievous. She wrote there is no i after the v. Lol. I’m not even sure which way I say it. They both sound ok to me.