As a person you never know which choices will be the most beneficial to you over time. Back in those days people underestimated the health hazards of working in the coal mines or didn't have a choice.
But your grandfather actually did have a choice, he could stay home and do jackshit. What do you think would have happened then? I'm fairly sure it would be a lot worse than if he didn't work his ass off. And thus your grandfather still gave your father some help even if it were only a few thousands euro's(did he have a house btw?) in your eyes and that even after he spend time in a care houses which he luckily could afford because of his hard work.
You should be proud of your grandfather and i'm fairly sure you are. But do not think of him as being stupid for ruining his life in the mines, he took his responsibility even if it looks retarded in your eyes.
My grandfather and grandmother of my fathers side suffered the same faith, he died before his pension age and she died at 51 after years of suffering because of the toxic fumes they inhaled during their life. Also because of the lack of knowledge about the health hazards of their work. They were self employed, worked their ass of and didn't have any savings when they died.
Hard work alone won't make you rich, and that goes for everyone, even for the bosses. There are a lot of people that do work hard, take risks and claim enough luck to aquire a decent amount of wealth and then to demand from these people that they have to pay a wealth tax after they already payed 33% bussiness tax(if they were self employed + the income tax on the wage they give themselves) and about 50% income tax is a fucking scam.