It all comes down to budgets. If they don't have donors and funders giving enough money for overhead costs, the reality is that they cannot accept and humanely meet the needs of all the stray and unwanted animals in town. Unfortunately, animal care and control isn't overrun with a surplus budget either.

I actually think it makes perfect sense to all involved. Destroy feral animals that would not make good pets and re-home animals that WOULD make good pets. If they spay/neuter and vaccinate them before adoption, then there will be fewer feral animals to deal with down the road. Thus, there would be less need to destroy animals, resulting in a more humane long-term solution. But they can't do ANY of this without more money, which in my eyes justifies the adoption fees. I doubt there are any suits sitting around in mansions that were bought with adoption fees.