It makes your site inaccessible to people who don't have TLS stacks. I can write and carefully audit an HTTP/1.0 client in a weekend; auditing even the bare minimum the code needed to speak TLS would take months or years.

What about the HTML 5 parsing, the CSS parsing and layout, and the JavaScript virtual machine? I doubt you could write and carefully audit all that in a weekend.

Most sites are already inaccessible to people who don't have modern web browsers, which all include a TLS stack.