Probably because he was only the drummer. I love Ringo, but was his drumming seriously good enough to cause him to be knighted? If he does indeed become knighted (and i'm all for it), its going to be because John and Paul wrothe a bunch of killer songs, not due to his drumming.
John, Paul, and George's lyrics are classic. But you have to take in consideration the overall composition. When I'm listening to a Beatles song, I pay a lot of attention to the instruments and how they contribute to the overall sound. Ringo's drum fills are so signature to the Beatles music. Ringo has said in his 2008 Off The Record interview that drum fills come naturally for him. They happen in the moment and are not planned.
"Before Ringo, drum stars were measured by their soloing ability and virtuosity. Ringo's popularity brought forth a new paradigm in how the public saw drummers. We started to see the drummer as an equal participant in the compositional aspect. One of Ringo's great qualities was that he composed unique, stylistic drum parts for The Beatles songs. His parts are so signature to the songs that you can listen to a Ringo drum part without the rest of the music and still identify the song." - Drummer Steve Smith (Journey)
Ringo "doesn't dazzle with flashy technique and pyrotechnics," says The Cars' lead guitarist, Elliot Easton. "What he does is so much more elusive and difficult: He plays songs on the drums. Anybody who has sat down behind a drum kit in the last 45 years owes him." (USA Today, Praising Ringo Starr, one drummer to another)
"Starr is vastly underrated. The drum fills on the song "A Day in the Life" are very complex things. You could take a great drummer today and say, 'I want it like that.' He wouldn't know what to do." - Drummer Phil Collins (The Making of Sgt. Pepper, 1992)
Kenny Arnoff -- "I consider him one of the greatest innovators of rock drumming and believe that he has been one of the greatest influences on rock drumming today... Ringo has influenced drummers more than they will ever realize or admit. Ringo laid down the fundamental rock beat that drummers are playing today and they probably don't even realize it. (Modern Drummer,Oct. 1987)
For being a Beatle, and one of the greatest drummers of all time, Ringo deserves recognition.
Some of Ringo's inconic drumming includes: