You can also get "I have a great mutt family/hunting/farm/whatever dog and I want another dog like this". They breed these dogs mainly for themselves and so actually do breeding work from thought out pairings and health checks to careful feeding and socializing. How rare this is depends on where you live and what's fasionable there.
There's a really cool breeding program for hunting dogs where they mix standard poodles (people forget they were bred for hunting water fowl and the 'silly' continental cut was to protect their joints from cold/injury while doing this task) and German short hair pointers. They're some of the most AWESOME dogs I've had the pleasure to work with. But because they're bred for a specific purpose they wont sell a puppy to anyone that doesn't pass their screenings. That's dog mixing done right.
People forget that a dogs temperament is encoded into their very genes.
Let's take the goldendoodle. The labradoodle too, just replace the golden with lab it's all the same point.
Sure goldens were originally bred as retriever dogs for hunting, same with poodles right? Sure. Maybe 50 or 40 years ago. Then they became the go to family dog and completely disintegrated their brains by destroying the gene pool. Dogs with actual hunting instincts were completely, utterly decimated by breeding for a good family temperament. Poodles on the other hand, at least when it comes to good breeders, were held to an intelligence standard and allowed to still do tasks.
So in comes the doodle. Most people when mixing dogs think 'oh this dog is x and this dog is y, put em together we get a dog with both x and y!!' But genetics is so much more complicated than that. You have 2 dogs with completely divergent genes, an aloof and independent well bred poodle (or a neurotic badly bred one, this worse but both bad.) And a completely dependant, food obsessed, retard of a dog the fucking golden as it stands today. What do you get? A confused dog that is prone to anxiety of all types, obesity, skeletal issues and a coat that can neither curl nor shed properly. Defeating the purpose of both breeds for something some people find cute.
There's also ungodly mixes like a German shepherd and corgi, (I've met 2 from the same 2 parents, the owners are asshole but they named them Frodo and Sam so... That's like half a point I guess. looks like the noble swedish valhund but with all shitty parts of the other 2.
To add to my first point and to end on a good note, there's also a lot of pug breeders breeding in jack russel to pugs to make them look more like their ancient ancestors. Now that's some mixing I can get behind.
