Why chef forcrd user to use hkp:// protocol for keyserver?

In apt_repository provider, I see below piece of code,

def install_key_from_keyserver(key = new_resource.key, keyserver = new_resource.keyserver)
cmd = “apt-key adv --recv"
cmd << " --keyserver-options http-proxy=#{new_resource.key_proxy}” if new_resource.key_proxy
cmd << " --keyserver "
cmd << if keyserver.start_with?(“hkp://”)

There are many people out there, who uses private debian repository like reprepro, and which keyserver is setup to work over http. So why to force someone with hkp ?
I agree hpk is standard, but is it wrong to use other protocol ?