You should use IO over RC if you dose Ca/Alk. The values in RC are way elevated (and inconsistent) and made for people with very low consumption who don’t want to dose and just supply Ca/Alk by doing water changes. But this results in Alk swings. It is not that IO is for fish tanks and RC is for reefs like a lot of people think.
Larger for-profit operations have different constraints and different advantages than the average hobbyist. They probably also don’t feed the best food, use the higher end pumps, care as much about smart controllers, care about how their tanks and stands look, etc. In short they treat it like a business, not a hobby.
For them, a little cheaper salt makes them a little more money in the large scales they go through. It doesn’t really matter if it takes longer to dissolve, leaves a residue, doesn’t have stable parameters after being made up, or has to be manually tested and supplemented before use when you are doing large batches used quickly in large systems with a professional staff.