[asoneth]

Just knowing about services like PC Part Picker and the management tools you mention requires time and expertise that people generally do not have before they build a computer, so "no real extra time investment" may only be true for someone who can amortize those upfront costs across many builds.

In my case I have built a couple PCs before, but it was so long ago that I'd have to re-learn which retailers are trustworthy, what the new connection standards are these days, etc. It's just not worth it to me to spend a dozen hours learning, specing, ordering, assembling, installing, configuring, etc to save a few hundred bucks.