It’s not enforceable precisely because the feature to enforce it hasn’t been built, and they’re phasing out the flash-based game. But when they build the replacement in HTML5, it’s easy to design and implement a configuration option like this. I program games as a hobby, and I know this from first hand experience.
Programmatically, it’s one additional condition to check, and one additional logical path for how the hand resolver flows, and one additional checkbox in the tournament designer. It’s probably maybe half a day’s worth of actual work, if that.
I can fully understand them not wanting to update the flash code that’s going away. And I can fully understand if they don’t want to implement every suggestion they get from the users. But that said, this is a reasonable, simple, and straightforward thing to do. They might have a lot of higher priority stuff to work on, but this is something that could be added to a backlog of work requests that they can triage, accept, or deny as they feel appropriate.