Personally I feel like makers saw an opportunity on 1) boost sales on new headphones 2) get rid of the cable hanging around.
I can understand and feel your fathers frustration trying to use wireless headphones, on the other side if they never ever get rid of the headphone jack then users are going to end up never getting trained on how to use wireless headphones.
Generally with leaps in tech there are leaps in reduced accessibility for older people, and with how fast tech is changing I can’t see the current older generation getting more familiar with tech.
Although give it a generation more and people that are currently 40 will be able to adapt new tech much easier and accessibility is going to be much less of an issue for the foreseen future.
Also at the end of the day I think there are adaptors that convert the jack into whatever port your phone has. I know it’s not ideal as you get more pieces to carry around and you might lose them but again there is a solution.
Also I have to state the fact that I was highly against not having a headphone jack as I own several pairs of good headphones with jacks and also I just didn’t like that change. I adapted and tbh I am much happier with Wirless headphones right now and not having those cables around me. Battery life could improve which am sure it will with time and I won’t need to charge them every so often but over all I am admitting that I was mistakenly thinking that wireless headphones and no jack sucks.