Because there are soft costs to integrating a completely different platform into your environments. What happens when you try to pass a VM from an Intel system over to an Epyc system? Unless they have the same instruction sets you can't pass them between different processors - meaning, you have to go in and manually find the greatest common denominator and disable the rest of the instructions that aren't mutually supported. That kind of thing.

Also, software is very often the largest cost for these systems. It's not hard to find yourself paying $100k a month for an Oracle license. A one-time expense of $50k for one piece of hardware vs another is barely a blip.

And in fact that hardware is often charged based on spec. So if you have 4x as many cores on Epyc, you will pay more in software costs on a monthly basis as well. That, or the software will simply refuse to use them until you buy an upgrade, meaning those extra cores are sitting there doing nothing.

It's counterintuitive to people whose experience is building a gaming desktop at home, but hardware expenses are not necessarily a big part of total cost of ownership for enterprise operators.