It would be interesting to know how much resource constraints are impacting their ability to build various things. For years, I-4 Ultimate contracts sucked up a ton of construction resources, then Epic sucked up a ton of resources, now we're back to Disney building things and I-4 is kicking off again with Beyond the Super Duper Ultimate or whatever name they're on by now. There's also a finite amount of creative resources that are, frankly, good enough to design and attractions like Unchained/BoTM/etc. and people are known to go between UC/WDI to follow the available work.
Typically there are always resources if you write a big enough check, but sometimes you just can't get the people or things you need and coasters are generally easier.