Why are there no number TLDs?
I haven't seen evil.666, programmer.1337 or nice.69, but could not find anything that prevents it. Is there really no interest?
Too confusing to parse vs IP address specifications. Can of worms no one sees a need to open.
Old rfcs used to prohibit labels starting with numbers. Although that rule isn't enforced; 336.net exists (used to be a blog, I think, is just parked now). I imagine ICANN might be reluctant to delegate a numeric TLD.