People are lazy. They get a dog and expect it to behave perfectly in crazy (to the dog!) environments with little to no training or exposure to said environment. The 1950s &60s saw an explosion of dogs as pets, continuing to this day, which caused this. Before then they were much more farm help, and working animals. Fast forward to today and dogs are part of the classic americana family and its expected to own one.
(Below is somewhat passionate, but a lot of info)
Pet homes didnt want the “craziness” of working dogs (only being driven mad by lack of work and stimulation, being tied up outside or backyard, and such) so then you get the explosion of pet dog reproducers* in it for the money angle - and now since 1990s and 2000s, creating “designer breeds”.
Lazy people + dogs bored out of their mind + not creating stable dogs but instead aiming for color or fur = a mess.
Theres a lot of awesome out there dont hear me wrong, but the entitled ignorant people who have dogs - and reproduce more dogs for profit - is a huge population subset and that creates issues.
Shelters that dont disclose bite history or behavioural issues (which is most of them sadly! This is actually a growing legal issue) giving an unsuspecting family or person far more than they can handle happens far too often too. This all creates chaos and is very new because, well, pre 1950s dogs were basically considered livestock, or for working purposes only, not pets.
Which is also very little time…your pet border collie has hundreds of years behind them working sheep, and you want it to be happy with a few walks now and then and wonder why its out of its mind and ya call it “neurotic” - whos the neurotic one really? Every breed has recent and long working history - but no one learns about that before getting their cute puppy. Yes your dauschund is gonna dig and tunnel and no you shouldnt and probably cant train that out. Why? Research what they were created for hundreds years ago.
But people want cute pets, to keep them in apartments or tied up in the yard when it annoys them, and give it basically no attention or stimulation; and still want the perfect-in-human-eyes behavior, able walking down a busy city street, show no signa of energy on a walk, be a Perfect Little Robot. Its not going to happen, its not fair to the dog, its not right in so many ways.
*I refuse to call such breeders, (ranty warning) because breeders will temperament match, heath check, these days that means OFA, genetics, thyroid pannel, and more, and none of this stuff or barely any does a reproducer creating for profit do because it costs a lot of money! Once litter is born a breeder will use ENS or Puppy Culture or similar to make sure they are being raised correctly - comfortable and stable in the human world as it is now. I have a huge rant on what a proper breeder is - and rescue too - because a lot of reacues are pretty shit as well (ex, regional herding dog rescue that buys from puppy mills and auctions because they cant keep up with the demand for the cute rescue pups - fueling the very worst of reproducers! But they get a pretty penny markup…)