Multiple reasons but convince/personal things really;
When I used two part I found the cost of preparatory aquarium versions of the chemicals expensive, (Bi Carb is Bi Carb, so to speak) so like most I purchased food grade, which was so cheap that I had to buy larger quantities to make the postage work out. This meant I was sitting on bloody kilos of powders, then the fuana trace bottles, that I had to store. Two or three dosing pump heads to calibrate, service etc. It was all just a bit bulky and time consuming.
Essentially storage of multiple components and the creation of stock solutions is/was far less convenient than one small powder pot.
I now make up half a litre which last me weeks, three scoops and were done. It isn’t as cheap, obviously, but with a small tank I’m on my second pot in a year. For me it’s just much simpler and a whole cupboard is freed up.
