Tickets may be cheap and somewhat eco-friendly if made from whatever recycled paper and a drilling machine like in the old days. But i doubt that's the case, so you have to account for the financial and ecological costs of all the electronics and magnetic tapes, and all the replacement parts you need to keep that system of control operating. Also, if your tickets are sufficiently unsophisticated to be eco-friendly, then they may well be very easy to forge.
That is, without mentioning that controllers have to be paid without providing any service. If you additionally take into consideration the social cost of the criminalization of something as banal as using public transports when you don't have money, the benefits of doing away with these systems of control arguably are even more evident.
"a fortune" is very relative. Railway workers are not exactly known to earn a fortune. From what i could see in France (quick search), they earn between 1500 (close to minimum wage) and 2500€ per month, before taxes.
Also around here i've never heard railway unions ask for better compensation, because as you have pointed out they already have a good pension and some transport-related privileges [0]. However, they have been relentlessly asking for better working conditions in order to provide a better service, and that the government stop to try and privatize railways.
Of course the managers, directors and private contractors earn a lot more and that's how our corrupt overlords get away with siphoning much public money into private pockets. But these people, we could well do without, and unions would certainly support a move like that.
[0] Personally, i would strongly approve better compensation for those people we now call "essential workers". It appears in a capitalist system, those who work the most and provide the most services (railway/construction/food/cleaning/health workers) are those paid the less and with the most grueling working conditions. That's a shame.
