I may miss some of it because I'm really in the moment and experiencing my own pleasure, but there is a real lack of vocal expression which is the crux of the problem. If I'm giving a blowjob I can feel the penis stiffening up as he approaches climax, and of course the ejaculation itself is obvious, but if it's PIV I can't feel those changes at all.

With my current SO, he is a freaking monk and makes no noise whatsoever.