They left out two most critical bits of info: power consumption and price. You can already get ridiculous amounts of x86 cores in a rack if you want, but those can get pricy to buy and to keep running.
Not all businesses need to write scalable software, because their current technology stack is just good enough and will always fit to one beefy machine, but on the other hand it will never fit on one ARM server module.
ps. hardware is cheap, while engineering work isn't
Where it gets tricky is if it's something written for an environment that itself has no ARM port yet, such as the JVM.
In long run having scalable software is win, but most of businesses will do just fine with unscalable software and good backup strategy, which they would need with ARMs anyways.