It's an ego thing. To have to admit that your hearing is going feels shameful and embarrassing, as it's a sign that you're getting old and your body is betraying you.
Or, he could very well be completely unaware that he's hard of hearing. I have some hearing loss, mostly in lower-frequency sounds, but I didn't realize it until I was screened. My voice is loud, and I have difficulty hearing people in crowds, and I usually have volume turned up so I can hear it (my phone is at max volume). But, I didn't realize that this was due to hearing loss.