Really, you think someone getting injured whilst being evacuated, potentially needing emergency services & bringing the whole system to a halt until they could be safely moved, whilst their fellow passengers looked on from an abandoned station waiting for a security guard to let them out would have less impact through the media? I think you are kidding yourself at best I'm sorry to say.
Sounds easy doesn't it? Just stop all services heading towards one of the North of England's busiest stations, making sure of course you don't end up stranding passengers coming from all over the region by doing so, then just walk the passengers along the now completely stopped tracks into the station.
Meanwhile back in reality, just making the area safe for an evacuation, i.e. stopping all incoming services in Piccadilly across the network, would easily take that long. Then you would have to ensure enough trained staff where available to a) Ensure all passengers safely disembark, b) are able to safely make the walk given that walking along tracks is not easy if you don't have the appropriate footwear, c) to ensure passengers don't wander off in the wrong direction, or become that person that knows better than the trained professionals, and finally d) to ensure all passengers have actually evacuated the train.
It is because of these safety reasons that this is rarely likely to be the first option, for lots of reasons. Firstly, and most importantly there is a greater risk of injury to passengers trackside. This should be blatantly obvious. Then there is the issue of actually stopping all trains to allow passengers to evacuate to the platforms. Piccadilly as you doubtless know is a very busy station, and even small delays through can have significant knock on effects on the whole of the local network. Stopping all trains for the best part of two hours will result in thousands of passengers milling around the station, not to mention the thousands of passengers now stuck on stopped trains around the region. Both of these could result in more problems, and even more self-evacuations from other trains, especially if people are on a stopped train watching other passengers being walked to the station. You could end up with the job being shut for hours, with people literally everywhere. And finally it is ensuring that if an evacuation becomes necessary, that there are sufficient, trackside trained staff to assist passengers who might be stressed or concerned by having to climb off a train and walk along the tracks.
This is why the first options are likely to be trying to fix & move the unit under its own power, then try to move it with a compliant unit or loco if available, all the while putting into place contingency plans to evacuate trackside as the very last resort. As I have said previously, I was once on a stopped train for over three hours following a collision. And during that time I spoke to the guard on a number of occasions about what the options where, and even volunteered to wander up and down the train keeping people up to date so that he could stay with the very distressed driver for longer. So I know first hand how frustrating it can get, but also how passenger safety is critical and why it is not a good idea to just tip punters onto the tracks without first exhausting all options that don't put them into additional risk.