Reliability, security, performance. Don't take my word for it http://www.apple.com/hotnews/thoughts-on-flash/
But please, do not take my word for it: http://truegryc.blogspot.pt/2010/05/response-to-thoughts-on-...
Remember the first iPhone didn't have an app store! It had a full(ish)-featured web browser that people were expected to write "apps" for. Apple continues to encourage developers to write web apps for the iPhone. They can hardly be threatened by a feature they actively promote and enable.
To the downvoter, you are a pitiful fanboy.