I'm not sure if that's still the case, but one of the main reasons were the publishing platforms and deadlines (@someone more knowledgeable, please correct me if I'm wrong!) :
As a game developer you'd need to set the publishing date weeks if not months in advance. Due to the store policies, missing that slot would result in another, potentially very expensive, delay.
Now, marketing is a significant part of the budget and you really want to sync your marketing campaign with the release date. Postponing the release by a few weeks is almost guaranteed to damage the sales drastically, to the point where it could kill your game before people even have a chance to learn about it.
You're late. So what do you do? You release all of your fixes in a huge day-0 patch. It's still better than the alternative.