by social contract, you mean?

No, just that banks borrow the money they lend from someone else again. Their banks after all, not just rich...

do even bankers that are low on the food chain get massive bonuses?

As far as I can tell, yes. Or at least much lower on the food chain than elsewhere. People I knew who started as lowly analysts in London already got high salaries, although they had to work their brains out. But the weird bonuses already started a little higher up the ladder.

Not multi-million or so, but still amounts most people would call a good year's income, and importantly depending on short-run performance.

That's what I never understood. I understand why CEOs can give themselves free money: there is no one above them in a position to stop them. Doesn't mean I like it, but I understand the mechanism to some extent.

But both for bankers and banks I don't understand.