Video games are still sold at retails stores (Target, Best Buy, ...). Those stores have to coordinate what is going to be on their shelves months in advance (6+)? So you promise your game will be ready and in a package and at their loading dock by November 15th. If you miss the deadline their shelf is empty of product since its spot was reserved for you.
Other customer electronics have similar issues. Promises are made to coordinate. They're generally made before the product is actually finished. Now a deadline exists. It's not trivial to change it.
The same is true for ads or was (TV ads in particular). They have to be scheduled well in advance. You pay for ads to run 6 months in advance because if you don't buy them in advance all the time slots will be sold out, no ads for you. But now you've added a deadline. If your product is not ready to buy when the ads run you've just wasted a bunch of money.
I agree that for many standard IT projects, deadlines can be kind of BS but I can also see why they tend to exist in retail products.
A solution could be, don't even start negotiating for shelf space before the product is 100% finished. Unfortunately few if any companies seem to be able to do this. For one, they need the money from the orders to make payroll. For another, if they waited until the product is done, then order ads and shelf space which won't be available for 6 months, what do they're employees do during those 6 months? They have no customers to fix bugs for yet. If the switch off the product to the next product there will be a big cost to pay to try to switch back the previous product they stopped working on 6 months previously when it actually ships and they need to actually support it.