To answer your question honestly, the reason is because "healthy" isn't a binary. There certainly are dogs that are so unhealthy they should not be bred. But on the other hand, there is no world in which all dogs are 100% healthy: if your goal is to say animals should not be bred unless they are 100% healthy, they'll go extinct! Making progress reduces suffering.

Efforts to breed healthier dogs should not be mutually exclusive with efforts to empty shelters. I envision a world where the shelters are empty too: I don't believe it's necessary to stop the efforts to have healthier dogs until after the shelters are empty. You can make progress on two fronts at once!

When you say dogs are beings, not toys or decorations, you run the risk of sounding accusatory. I believe we have goals in common and could learn from each other without resorting to villainizing.