Why are so many bikes designed in such a way that the pillion is uncomfortable?

I am a 5'10 guy. I want to buy a bike so that even my 60 year old mom could sit behind me but I don't see many options. The only ones I see are the cruiser bikes but they are just soo stupidly loud that I can't see myself ever buying one. I don't care about bike sound like at all. It just feels attention seeking to me. What bike can I still go for that isn't loud but has pillion comfort as well?