There is no indication that this change is happening to allow extended engineering access or similar (if so, no-one has piped up!); it's a purely penny-pinching move done to give the appearance of doing 'something' to save money. How much will this realistically save?Extending that argument, why not have a service all night, on all lines, for the passengers that might use it then?
The point is that there are very few passengers on the last trains down the MML. We can’t, indeed shouldn’t, try to provide a railway service that is convenient for everyone‘s transport needs all the time. A line has to be drawn somewhere, and sometimes that line needs to move.
You also have to wonder why other lines continue to enjoy similarly timed first and last services. And why, at the very least, the 23:35 to Nottingham can't be extended to Derby in passenger service, rather than running ECS.