The 'reason' needs to go in the OPS log - citing 'Operational' is absolutely fine and more than meets the needs of our curiosity.
As an operational centre we will never refuse your request, although you might be on a sticky wicket later on as there are some airports that will only accept you as a diversion in case of emergency.
IIRC EDDF will only accept diversions from EDFE if they declare emergency for example.......
Telling us the reason will also help us to dictate the priority we give to your request..... in busy traffic an 'operational' diversion may well not be at the top of the pile of things to do, whereas a medical diversion etc will obviously get processed ASAP.