This is a slightly better question when you know that most food brands in a US grocery store belong to one of a much smaller number (3? 4?) of companies. So the brands are about more than just "people want different kinds of food". They appear to exist for their own sake, independently of how many kinds of food there should be.
Dogs are kids without the sacrfice. A dog will never say he hates you, will not put you through nine months of pregnancy and labor to have, won't force you to give up your career pushing spreadsheets/work lots of overtime hours, won't force you to move for a bigger house or a better school system, and won't end up being a disappointment or worse. You can kennel them to go on your vacations and they will never ruin them by getting sick or sucking all of the fun out of it. They just sit there, look furry, show affection, and occasionally chew up your furniture, poop on the floor, and bark.
Apparently, this is not so crazy as it seems. Especially in cities where real estate is expensive, people put off having kids for longer, and make do with pets in the meantime.
