It's the same as when a programmer will constantly re-factor their code to provide better abstractions or improve efficiency. Or when a designer spends hours deciding on how to a lay an interface out.
The tools to create generic copy-paste movies and music are already out there in the same way you can build a website by buying something from template monster and copy pasting a bunch of Javascript and PHP that you found on google around.
Of course tools will get better and make efficiency better but all that will do is raise the bar. People want to see movies that will wow them , either with better special effects than they have seen before or with clever/funny dialogue etc.
The people who have the skills to do this best will want to work for the big media companies because these are the ones who will open their wallets and pay them a good salary to do what they love all day with the best tools available.
That's were your wrong. Computers don't understand beauty, but given enough processing power, and sample data they can recreate it.
There's already a program that can listen to Beethoven and reproduce something that even experts can't tell he didn't write.
A movie example: In your movie creator you set up a scene with 2 people talking in a room. The computer has been trained with thousands of such scenes, so it automatically selects the best camera angles and allows the operator some manual control. That will happen at some point.
Indie movies will upload their back yard or buy stock trees, and it will show. That's what separates big budget from small budget - perfectionism and meticulous attention to the tiniest details. Computers doesn't understand beauty or emotion, so you need fine grained human control every step of the way.
It's the composition that is expensive and not the ability to perfectly reproduce reality.