Why is OCB-AES mode not becoming a standard for authenticated encryption?
Because OCB is patented.

And there are other good solutions for authenticated encryption that aren't patented.  This makes them more suitable, in most situations.  I can recommend, e.g., EAX, GCM, or CWC.  EAX and GCM have been used in some standards, and AES-GCM has been standardized.

For pointers where you can learn more, read Wikipedia.  And try using search on this site with the phrase "authenticated encryption".



Update: There are now free licenses available for OCB.  However, they have some unusual restrictions, which some implementors have expressed concerns over (e.g., one license only applies to open-source software; another allows only non-military uses).  For a detailed discussion, see the responses on this thread on the IRTF CFRG mailing list.