The bottom line is companies do not take on contracts that will generate them a loss. Whether a profit is derived from creative accounting, which is a very common occurrence especially in public tenders, through subsidies or just actually doing well they, as we are often reminded on here, do not do it for the betterment of humanity. So if companies, even if there were only 3, lined up to bid for the Northern franchise then there is clearly a profit to be made, otherwise none would have bothered. Arriva, as has been pointed out, isn't doing too badly, and since the referendum vote DB have backed away from partially floating it so they must be sure that it isn't going to be a loss to their group, and are able to keep it on rather than take a possible lower floatation price for it.
I never understand why some people feel the need to back big business over the people actually delivering the service and helping generate the profits. Northern staff may not yet have contributed much to those profits, but many of them helped the previous franchise shoehorn in up to 25% more punters onto their ever-aging trains, whilst actually managing to improve the service from the previous owners (ironically Arriva). They have managed despite lots of bad publicity over trains, capacity etc to deliver more than might have been otherwise expected.
On face value, the offer may look reasonable, being a fraction above inflation. But I don't know what they are actually on, the full nature of the offer, or the nature of previous deals. But even if it was a reasonable one, simply testing the waters with a ballot isn't some despicable act of greed. Unions use this all the time to see if there is any flexibility in the employers. They must at least get a sense, as will Arriva if the staff are unhappy with the current deal they have and if the offer will make up anything lost previously. Perhaps those staff actually working for Northern might offer some insight as to how they are feeling about their pay and T&Cs, rather than some board members simply huffing and puffing about how terrible it is that some people want better?