A lot more traffic than you can imagine comes over UDP. Most Bittorrent traffic (used to be a majority of traffic on the Internet!) comes over LEDBAT, which runs over UDP, https://tools.ietf.org/html/rfc6817. WebRTC by Google is now using UDP for most things, because NAT traversal is not really possible over TCP (due to the 3-way handshake, and the SYN-SYN connection setup not being widely supported by OSes).