Annual franchises will most likely have less than a year of development time, which doesn't developers enough opportunity to fine tune any bugs they come across.
This can greatly damage the franchise's reputation, as well as the company's itself -- making both a laughing stock among the gaming community. (Looking at you, Assassin's Creed Unity.) And that's something no one wants to see.
Developers should scatter their releases, offering a new game around the winter season and an annual release the following spring/summer, giving gamers enough time to sink their teeth into the latest IP.