Exclusives led by platform holders usually have a LOT more investment than flat multiplatform games, giving devs more resources to play with.
Every platform holder has its own set of rules and while they can be bent, usually aren't. This will help devs with freedom of creativity with a singular set of rules.
Focusing on a single piece of hardware gives devs more room to breathe, better methods of testing, bug reporting, refactoring and flat out allows all devs to give full attention to the game vs spreading them out between teams for multiple platforms.
Access to specialized tools you can use just for that platform.
Quality of content aside, a platform holder led exclusive will always have the upper hand in almost every way during development.
There is no getting around this.