1.
I think I don't do it because I want a separate life from the product. I don't really want to encourage people to think they have access to "me". I have a "support" page for that. I value my privacy.
2.
Software is rarely written by "one guy" anymore. Its a really complicated thing that might involve contractors, 3rd party libraries, and maybe we don't want to reveal our sources anymore. Credit is a thing that goes far beyond the company's creation of the product. For one product I sell, I do have an Acknowledgments section included in the documentation.
3.
Listing developers on the website is fine, that can be changed as staff come and go. But embedding "John Doe" within the About page (desktop app) may not reflect the real people behind the application five years from now. Yes, in some markets, it can last that long before an upgrade.
Maybe it would improve things, maybe it wouldn't, whatever, but that's my reasoning. If something won't improve sales, then I'm not inclined to do it.