That's not a retrofit either. With a multi tool those can be removed with a few bolts. The ones on that bench are single mold cast iron. You'd need an angle grinder to remove those, not that any law abiding good citizen would.
So dumb. They could have spent the extra money helping the people they don't want sleeping on benches not sleep on benches. Most people probably agree, just not in their backyard or with their tax dollars. The amount of work they're willing to put in not to help someone is absolutely astounding.