Private policing predates public policing,[0] and so asserting that this is is a new development is not really correct. The same is true, incidentally, of firefighting: private insurance companies formed their own private brigades to protect their policyholders' property.[1] Lots of things that we tend to think of as "naturally" public services have only very recently taken that form.

[0] See p. 1193 et seq. of this article: https://law.stanford.edu/wp-content/uploads/sites/default/fi...

[1] https://en.wikipedia.org/wiki/History_of_firefighting#Early_...