The honest truth is all it takes is a simple walk down the street to realize some big dogs see little furry things like Yorkies and Poms as prey, cuing predatory behavior. I'm sure the big dog owners would understand more if they had to walk their big dogs among still larger animals such as mountain lions/cougars who saw their dogs as prey and apt to come for them at any time. Then they might understand what it feels like to have something you feel like you're putting in jeopardy by just venturing out with your tiny dog!
Any city that makes a park for dogs who doesn't recognize that some of the larger ones will see the little ones as prey isn't very dog-savvy and might need to check with the ASPCA on the subject of how some large dogs might react around smaller dogs and take all the precautions they can to give the little guys a break and keep them safe.
Dog Parks | ASPCA Predatory Behavior in Dogs | ASPCA