Why Kong 1.x not support L7 Routes for destination port?

What is the reason why L7 Route can not match destination port ?

and why Route matching uses the destination port ?

if ngx.config.subsystem == "http" then
    function self.exec(ngx)
      local var = ngx.var

      local req_method = ngx.req.get_method()
      local req_uri = var.request_uri
      local req_host = var.http_host or ""
      local src_ip = var.remote_addr
      local src_port = tonumber(var.remote_port, 10)
      local dst_ip = var.server_addr
      local dst_port = tonumber(var.server_port, 10)
      local sni = var.ssl_server_name