I'm not too sure why. When I started with my current project, I ended up getting a whole bunch of 10/13 g1/4 parts, intending to use them. It wasn't until I had them in my hand that I realized how gigantic they are and swapped them out for a smaller size.Interesting... they are probably within walking distance from where I am! Small world... The thing I don't get though in the context of SFF is the unquestioned predominance of 10mm ID tubing and G1/4 ports, and it shows in their design: All you need to go through a GPU as the most heat-emitting part with a normal pump is about 18 mm² of fluid cross-section - ironically most water blocks don't provide any more at their bottlenecks. That means even 6mm ID tubing and G1/8 fittings are brutally oversized. I think that what we are looking at in most builds, and also their parts, is an unchallenged paradigm rooted in the aesthetics of big builds themed around tubing - engineering wise none of it does make much sense (same as the one-120mm-rad-per-component rule of thumb), and is low-hanging fruit for space optimisation.