Same with my local shelter. They're always full of dogs & cats, with a wait list to get in, & they work at it regularly to promote adoptions, like taking some to Petco & other locations. (It's a no-kill shelter.) The problem is that there aren't enough good homes to go around, & when some people are told the shelter cannot accept the animal they want to turn in right away, they just dump it somewhere.
It's not fair to the animals (domestic pets do not live "happily ever after" in the wild- they face hunger, disease, temperature extremes, predators, etc.) nor to sympathetic but overwhelmed pet lovers, or people who are tired of cat-fights keeping them awake at nights, & cats roaming in their yard, etc.