How so? You would still need to take it back in order to adopt and that way the shelter wouldn't be overflowing with animals, plus it would be possible to see if they're good with animals
HEAR ME OUT ON A NEW IDEA: PET SHELTERS LET SOMEONE BORROW THE ANIMAL; SOMEONE COULD BORROW A CAT IF THEY HAVE A MOUSE PROBLEM OR BORROW A DOG IF THEY FEEL UNSAFE WALKING
THEY'RE REQUIRED TO TAKE CARE OF THE ANIMAL AND IF THEY GET ATTACHED TO THE ANIMAL, THEY CAN CHOOSE TO ADOPT IT