From a business's point of view, it is a Bad Idea to just keep expanding while leaving some park areas underutilized. The underutilized areas/attractions aren't bringing in guests, but yet, they're costing the company for operation and maintenance.
GMR needed a huge capital expenditure to update it. So, they decided to spend the money on something new that (I guess) they thought would be more popular and "more Disney." SWL is replacing a moribund Back Lot ride and outdoors studio set and expensive car stunt show. Pandora replaced a place-holding 'temporary' camp Mickey. Ellen's Energy became a joke as a nap ride and it, too, needed big bugs to update the worn down set pieces. Keeping that while building new somewhere else is just bad business.
That being said, the blessing of size did make an appearance: The DHS project expanded into the swamps with the extra parking and the SW Resort. And its footprint was increased recently with Sunset Showcase and with TSL taking over actual back. Ratatouille and GotG and the UK ride are expanding Epcot's footprint. TRON is expanding MK's.