It was the right call. AIM was losing money with no obvious way to monetize it. AOL was not in the same position than Microsoft was. They had little experience selling to pro customers and they were bleeding users to Google Talk and Facebook Messenger at the time.
Even knowing that the mobile market would explose in popularity, it is far from obvious that AIM would have even been positionned to benefit from it. Google Talk was really popular then and notoriously failed to convert that into a leading position in the mobile market.