That does make sense but what about all of the people here who like to modify their stuff and build from scratch? Even on the craziest custom machines I have mostly seen off the shelf PC parts only. The machines that don't even use PC cases are still using PC radiators. I guess it's still easier to use purpose made stuff for those machines but at some point there has to be a guy who needs more heat exchanging capacity than he needs quick compatibility, who decides to step up an order of magnitude and use something that was designed to move a huge amount of heat (relative to a custom PC cooling loop). Where are those guys?
It has to do with a combination of several things.
For starters, a special "out-of-the-box-thinking" mindset, being able to "see" the potential for other uses of things besides what they are build/created for.
Example, an old (rusted) BBQ grill can still serve as a crude sieve to prevent large objects from entering a drain hole.
You preferably have to be able to "build" the whole thing in your mind.
Most things "evolve" around some idea/object:
"I can use this, and add that, so i get that and then i add that; but then i need to resolve the problem this creates"
This builds a whole contraption on top of a (potentially flawed) idea.
You also need to be able to do iterative thinking in that case.
You preferably have to be able to backpedal a bit and improve the previous steps.
At some point you need to go back and say :
"i've build all this on that foundation, can i not find a foundation which is better suited for what i want to achieve?"
It means that not only you have to be able to build the whole thing in your head, but also the be able to build the variations in parallel. And cut out the needless convoluted intermediate contraptions.
Not a lot of people can do this, most people start of in one direction and never look back and /or question the path they've chosen. While persistence is a good thing, blind stubborness isn't, as you end up where you didn't want to go.
It helps to know what has been done before, to have some materials knowledge, the limits of those materials & the limits of the laws of physics. It keeps one from galloping straight into the abyss.
Its engineering genius bordering on insanity, it helps if your name is Leonardo or Panemarenko
Add to that Time, Budget & convenience
Example_1: for a heater core, i could look up all nearby scrapyards in the yellow pages. Then visit them one by one bringin my trusty crowbar & screwdriver along, and dismantle each & every car,truck, item which looks promising.
Or, i could just go to an automotive center and order the core i need.
Or, i could go to a watercooling site and order the rad i need.
Example_2: Barbs & fittings: a "specialist" WC website/shop in another part of the world, or you local hardware/plumbing supplies store?
It comes down to what you want to pay in Time or Money
Doing one would save time, but will probably be more expensive. Doing the other costs time, but gives "fun" by rambling through scrapyard or wandering through the aisles of the HW store
So, you can see amazing builds centered around some mundane, common parts and ask yourself why this ordinary plain thing is there.
Its either because of :
-that part serves the purpose so well that it doesn't need to be replaced; even thou it looks "out of place"
-the builder wasn't able to look beyond the purpose or alternatives to the object
-time/budget constrains played a role in that step
-plain laziness
or a combination thereoff.
Note, all this weird tinking is not to be confused with the marketing department telling engineering that they've announced they'll start selling product XYZ in 3 months and that surely those 3 extra months are enough for engineering to finally solve the little problem of requiring nuclear fission in a shoebox sized contraption to power product XYZ
