Completely and obviously false (the part about everything in business is about sales). It's not as sexy, but often policies are about reducing costs. Like changing suppliers to save a few pennies per item.
If it were all about sales, then I could buy widgets for $100 a unit, sell them for $50 a unit, and call it a success.
Obviously positioning matters too (hence all the garbage food at checkout), but I wouldn't by default assume that this is the case, and especially not the only driver, behind dairy placement.