Remove the instance cap and replace it with diminishing returns.
Example. You hit 30 instances in a day and the XP drops 5% each run after, loot drops 50% less etc…
There are many ways of dealing with this that isn’t a hard OFF switch.
Seems like “What ever takes less work” was the method blizz choose.
I don’t like the idea of either but since we have one… why not improve it.
This does nothing to people one pulling ZG trash and exploiting the bridge pathing, or similar. This is clearly something they wanted to hit.
Clearly this was designed to be a quick blanket fix to something specific they were concerned about until they want to delve into it further.
I expect them to either lift it at some point, or add some more general solution to whatever their real concern is.
Well either way, this is an idea. As for "“doing nothing” that just simply isn’t true.
I imagine they added a single blanket restriction, rather a series of complex restrictions.
I mean we’re talking about the same devs that can’t even add a way for us to tell how many instances we ran today. 
I imagine anything else they’d do would backfire even harder.
Lots of level 60s sell runs. They get gold for them. They only care about the gold and nothing else. How will you diminish the gold?
Or chose not to do that. Do you seriously imagine they “can’t”? I’m sure most or all of the devs “can”.
Devs don’t decide what features to add to the game. You don’t have 200 people randomly making changes to the game, based on what each of them likes. That’s insanity, not a game company.
Whoever decided to set the instance cap (for exploiters) chose NOT to make this feature easier for exploiters. Why would they? Why would they add a feature to help make an action easier, if that is the action they are trying to discourage? Blizzard doesn’t think normal players hit that cap. So no normal players would use that feature.
Blizzard is not about to recode huge parts of the game to deal with botters when the 30 instance cap doesn’t even affect most people.