This is actually your answer, in case you ever wanted to know:
Walk into any toy store or major retail chain with a toy section. Count the number of toys you see for:
Toy Story (any)
A Bug's Life
Monsters, Inc.
Finding Nemo
The Incredibles
Ratatouille
WALL-E
Up
Brave
The number is probably very low, and would be at 0 if Monsters University had been 3 months past the home video release. You know what you'll have no trouble finding in the toy department?
Cars toys.
You know what franchise you'll also find perennially in the bookbags, shoes, and lunch bag/thermos section?
Again, Cars.
Pixar keeps making them because the toys sell all year long, and probably see a sizable boost when another movie hits. I mean, this is a company that pushes boundaries as to what can be done in a 3D movie; take a look at the environments in The Incredibles, fur rendering (including impacts of collapsible particle-laden objects) in Monsters, Inc., and even the boundary/portal tricks used in Presto. Cars, from what I can gather, is probably the project Pixar trains new staff members on, because it's the definition of a safe film.
Chances are, the franchise pays for itself and has no bearing on the release of their major feature films.