Building your own is cheaper, although not by a ton. Valve isn't taking a loss on them.
I've built two PCs in the last 5 years and both have had parts that were broken from the factory... There is something to be said about being able to hand off troubleshooting and replacement. I had ASRock pointing fingers at everything else to the point where I had swapped out CPU, PSU, and RAM, until they relented and replaced the motherboard (the replacement which is broken again now 5 years later by the way...)
Do you trust the brand and models of the gear you're buying? Use Newegg for reviews even if you buy from Amazon?
Though if a component dies due to ESD from an imperceptible spark then the manufacturer skimped on ESD testing