Wizofoz nearly got it 100% right.
Yes loco's have put the big players under pressure but also more astutely, they have put out their maintenance to the cheapest provider.
How many loco's have their own maintenance as 100% part of their own company.
By doing it this way you put pressure on everybody but yourself.
You will then always get the cheapest but leave question marks about the quality.
Add to that the no delay bonus, ensuring that the self centered captains among us tend not to enter too much in the tech log and are we increasing or decreasing the safety margin?
So basically LOCO's screw everyone.