They know they can just dump whatever shit out and people will keep giving them money is the real answer

The last few marvel movies (spider-man excepting) proves the lie of that statement.

Unfinished script doesn't mean directionless. Also this is why films have reshoots. Sometimes you have an idea, film it, and then have to change it. Sometimes you don't have an idea, but in the moment, in the scene you figure it out.

Plus they've been doing this since the days of Community,

"Joe Russo said, 'Let's just cast stars if we can spot them.' You know, let's not worry about who fits the character or what you had in mind; let's just cast people that are clearly going to be stars. And that's a very — the Russo brothers were geniuses in casting. And Donald was a figure that they put in front of me, and then I immediately said, 'Yeah. Absolutely.' And he was clearly a genius. And I've often told stories about how we would, literally, the writers room would, if we were operating at a fast enough pace, we would put at the end of a scene, 'And then Donald says something funny.'"