They don't get it
These large companies don't get it.
There's equal "proof" that remote/work from home people are as good, if not better than those in office teams. They will be better, if experienced and good skill in their job function, than those in offices. The reason being less distractions from colleagues, apart from the cat of course.
They also may work slightly long hours, because they can, and often more productive.
I bet there are stats that the employees are after to either prove or disprove the benefits. These need to be complete stats. I've seen companies try this, but never ever give evidence to employees to show that it "needs" to be done.
This move will almost certainly have the opposite affect, since good people will leave causing them (IBM) massive issues.
Well done IBM