Not 100%, no, but I believe they wished to shape player behavior using this change because they didn’t like that people were doing so many instances. It did not fit what they believed was in the “spirit” of vanilla.
Having played WoW for 15 years, I know full well what Blizzard is like. They HATE when people play their game a lot. They punish people who play more than others, because they want the people who play less to feel safe and fuzzy. That’s exactly why the vast majority of people you see supporting this change are super casuals espousing their hatred of the hardcore. “lol nolifers doing 30 instances a day? QQ”
They almost all complain that people who do 30+ instances a day are ruining the game. So yes, I believe the change was done with targeting legitimate players in mind.