It's got a lot to do with appetite for risk. If you've got nothing to lose, you can do all kinds of crazy wonderful stuff, but if you've got a LOT at stake, that's when you start making predictable, safe movies. By including everyone from 'The Avengers' in 'Captain America : Civil War', and by using the same directors as the one before that, and making sure it continues into 'Infinity War', Marvel is basically outlining the movie(s) they want to make, which is the movies they made last time, and which are being propelled along a path that is unstoppable and inevitable. And why wouldn't you do that, if just by not doing anything stupid you can make an easy billion dollars?
That, in a roundabout way ,that replaces a shorterm risk of failure with a longterm risk of boredom and stale-ness and predictability. Then again, every studio would rather have a billion dollars today than take a risk and get 2billion in three or four years. To be fair, if I was running a business, I'd be doing that too.
But I'm not a business. I am a movie-goer. And I don't really want to watch the kind of movies that Marvel is suggesting they're going to make with cold, calculated precision.
That's why part of me actually is looking forward to Man of Steel 2. That movie could be genuinely, gloriously mad. Because DC is desperate. And desperate people take risks. Avengers 2.5 : Civil War might end up being many things, but gloriously mad will almost certainly not be one of them.