There is nothing wrong with 2 part or 3 part just as there is nothing wrong with Kalkwasser. Not to state the obvious but some hobbyist like to tinker and additive based methods may scratch that itch. Others like simpler solutions that maybe All For Reef brings and budget accordingly. Some like to mix things up and find a combination that works.
The part I find rather interesting is those who use a product or method in ways that it wasn't designed for. Sort of like the right tool for the job. The hammer or screwdriver isn't always the right choice. Ok, there is one exception. F4 tape. That is always the right option...
But I ramble...