Beethoven is deaf. This means he may not be able to hear something dangerous coming to injure/kill him. Therefore, he is very vulnerable of being killed by Flippy when he's not watching his back. His deafness also makes him unaware of other tree friends dying around him when he's not looking as well. Beethoven has a quite successful musical career, as a conductor and performer.
Beethoven was deaf in reality like in HTF world. The real Beethoven died on March 26 1827.