There are also logical reasons for evening services being a different operator. For instance, High Peak run some Macclesfield locals in the daytime. If Cheshire East decides to contract an evening 14 then High Peak wouldn't be able to interwork it and would need to send a vehicle back to their depot very late along the Car and Fiddle, which may create problems in winter.
You can also have a big operator using large buses on the daytime service, and it wouldn't be financially viable for them to use a 40 seater on an evening service, or for them to acquire a solitary small bus for that contract.
