It saves them money and makes use of existing stuff instead of having to build new.
No. No. And again, No. It's cheaper if we just electrocute to death everybody ever found guilty of a crime. Why don't we just electrocute them all instead of having to build those big, expensive prisons and feed people? Hell, does it even matter that they're guilty of having forgotten to pay for their livestock purchase within 24 hours?
When it comes to the police, cheaper is not necessarily better. I would rather not have police plowing through mine or my neighbor's door with an MRAP. We aren't in a war zone, the police aren't the military, and there is zero justification to make everybody feel like we're living without rights and freedoms under martial law. Some studies have shown that when police are less aggressive (possible even not carrying guns) and laws are toned down from the "let's be tough on crime and send people away to jail for 10 years for carrying around a little dead leaf in their pocket", that violence between the police and the populace also goes down.
Accountants and MBA's tend to be only concerned with financial costs and ignore the other, real costs. Surely you're not one of those? :-)