I'm no fan of Macs, but I suspect the so-called relibility of Macs is due to the fact that there aren't thousands of OEMs building them. If you limit the variability of a product, you can debug it.
As partial proof of this theory, I offer some comments made on another thread -- that during the brief period when Appled licensed other manufacturers, their product was unreliable.
I also build my own PCs and have never experienced any of the reliability problems everyone shouts about. The competition get something on the market at a price point has got to cause problems. If I'm building somethng and can't afford the components I want, I simply leave something out and save it for later.
They did that for a time about 10 years ago. Several upstarts jumped in, but it was probably too late by the time they did. Apple cancelled the program and bought back the licenses.