There's a few reasons
(1) more cost effective
(2) less pin volume
(3) takes up less space
(4) higher quality product
Lets say you get SUS500, and you want to dilute to SUS250. You dilute it 1:1 with pharmaceutical grade MCT oil (which i just linked) and you know at least 1/2 of it contains pharmaceutical grade MCT oil. You don't know what quality oil vendors use (how old it's been etc, peroxide value etc). But when you dilute it, you know 1/2 of the oil is very high quality (+1/2 unknown MCT) vs just buying SUS250 and hoping they used some good shit to brew.
The downside is that HC gear has more solvents, and you pray that vendors know wtf they are doing and are actually using solvent resistant brewing gear and not some cheap setup that leeches slowly into the oil.
Trade offs i guess.