Popular animated movies used to belong only to Disney, and they released them sparingly, not wanting to step on the toes of their own product. However, once Disney/Pixar became a force to reckon with, Disney was releasing CGI films on top of its own traditionally animated films, and began crowding the schedule with more films each year. These days, animated films crowd theaters with offerings from Disney/Pixar, Sony Imageworks, Dreamworks Animation, Warner Bros., and Paramount/Nickelodeon. It's a jungle out there -- or a forest, or a farmyard, or ... well, you get the idea.
This is typical of the Hollywood "me too!" syndrome that hits when something works well and starts making tons of money for a studio. Everyone else wants in on it. Horror films started making money, so now everyone is putting out a lot of horror movies. The Lord of the Rings opened the door for more fantasy films like The Chronicles of Narnia, and Eragon, and the popularity of X-Men gave rise to a slew of comic book movies including Spider-Man, Superman Returns and the upcoming Ghost Rider.
Animated films have always been a treasure for younger and older audiences alike, and are part of a dwindling part of the theater experience that people can still enjoy as a family. Are you still going to see animated movies?
Other animation on Cinematical:
The Demise of Hand-Drawn Animation
Studios Still Don't Get Animation
Dreamworks Choosing Quantity over Quality
Golden Globes Adds Animation Award