But that same argument applies in the other direction -- converting to a new system is costly and creates possible points of failure when/if the conversion isn't done correctly.
It's great to say "we should all use the same system" -- there are certainly advantages to standardization. But there are also costs to conversion, and as in most things there are arguments to be made in favor of both system A and system B.
A more balanced approach might be "we should all be comfortable with conversion, and use whatever system suits us best locally", which is exactly the same approach we apply to language, laws, and 1000 other things.