>> most of those "primadona devs", as you call them, would much prefer to write well-designed programs cleanly coded

Most of them - yes. But there's a non-negligible chunk of them who are too careless or incompetent to care about quality - they've been around long enough to gain knowledge about project and get Vice-President title(inflated ego included).

It is especially visible in big banks (I suppose it's typical for other big non-tech corps as well) where tech culture is generally on poor side.

edit: grammar

Given the chance I'd likely collect a fat paycheck and bail out at the end of the contract as those other people did. But that attitude is responsible for the increasingly awful mess that modern software is becoming.

Almost everyone is at fault, me included. The perverted incentives of today's world are only making things worse.