Planning out a project is.. pretty hard.. even when you have shipped multiple titles, its still allot of guessing how much time some stuff takes. I mean things might fit perfectly on paper, but when you start developing you encounter tons of stuff you couldn't possibly have predicted. If you develop for Publishers who aren't EA, Activision or any of the big boys, then you can get away with moving deadlines around a bit. But generally, when something goes wrong, there is no room for error, and especially if you make a big game, you probably have a launch date already set out, tons of stuff gets arranged around that date, so if suddenly you can't make the deadline, then shit.. you need to crunch! plus if you create so called AAA games, you have events to consider that get thrown in by publishers only weeks before the event. for example E3, Pax, etc.
Unions have pro and cons. and one of the biggest cons is that it makes employee's who joined a union a liability. It wont stop insane crunch because those studio's simply get the cheaper juniors who haven't joined a union and it will work for them, and soon you won't even get a job if you have joined a union. developers will avoid you like the plague.