Because the value of IP is stored in cultural zeitgeist. People don't want to go to "A mouses fantasy location" they want to go to Disneyland.
Convincing people to give a shit about your IP is a totally different issue to producing it, in my opinion. There are already countless talented artists a big producer could hire to make them new IPs but it is still incredibly rare for a new IP to take off.
Art keeps getting cheaper and easier to make yet as a society we are addicted to remakes and expanded universes, new seasons of shows that ended a decade ago etc.
