The answer lies in the question
In all seriousness though, I think it has to do with the “big brother, little brother” image that exists between the two companies. For so many years Universal was seen as the weaker resort, an afterthought to a family’s “Disney vacation”. Since Potter in 2010, Universal has gained massive notoriety, stealing market share and fans from WDW. The resort has “grown up” per say, and thus the two fan bases kinda argue over which is better, as if they were two rival sports teams.
It’s a stupid beef amongst fans, but a great one to have between the two resorts. Both sides tend to put out their best work when the other one is trying to steal vacation bookings from each other.
To me, it’s no coincidence that Hagrid & RoTR open in the same year, or that WDW’s 50th will be competing against possibly the best coaster in Orlando when the JP Coaster opens.