The same reason ipv6 still isn’t standard, there are tens of billions of networked devices in operation, with tens of millions being added every year above replacement rate. Any new network protocol or standard needs to integrate with the current stack to be adopted even a little bit; because corpos aren’t going to change out or update the 40-60 year old pieces of their stack that run well enough to not hinder profitability.

The bottom line is and always will be in almost any industry some variation of “we already set up hardware that was developed solely to use this ancient thing that’s a standard. Once this new thing becomes industry standard, then we’ll switch.” With the big issue there being, the industry standard will never change until somebody makes the first change and nobody wants to risk the amount of money it would cost to switch.