"First of all, although it's “cool” to build your own computer"
Steven, that really glosses over the reasons why people build. Honestly it's annoying coming from someone who works for a tech/PC enthusiast site. I've built rigs over the years for a variety of reasons but being cool was never among them. Setting aside the reasons I started, the main reasons I continue to build are cost and component selection. If I could find a prebuilt that was affordable, upgradable, AND used top-quality components, I would.
I've looked around over the years and only the boutique vendors really use/offer premium motherboards, RAM, storage, and cooling - and only on their premium models. When configured with decent parts, the cost is somewhat high, although it's understandable when you look at all the factors involved in a boutique PC shop. Meanwhile, all of the more affordable mass-produced or the entry level semi-boutique systems heavily rely on preconfigured primary components and basically rely on just-good-enough parts.
When I look at something reasonably priced, I can't help but look at all the components I'd want to swap out, and in the end I decide I should just build again. Obviously if you don't have the ability or time, you need someone else to build it for you. But if someone tells me they're going to spend $1300+ on an MSI mass-built machine, I'd probably suggest they first look at a few of the boutique builders.