Why did they put the Chipettes in the second film?
They could've easily of had a spin-off after the first Alvin film and then mix their "spin-off" with the second Alvin film, which sets the events on how they knew about the Chipmunks and Ian.
Or after the sqeakquel (which would've been a different plot), then make the spin off.. OR EVEN after a trilogy of ONLY CHIPMUNKS films, have a spin-off for the Chipettes and put them in the fourth film which could've been the plot of Squeakquel, the fifth film would've had the events of Chipwrecked.
They could've made so much more money that way! What a wasted opportunity.