You have to spec out the parts, ensuring compatibility. Manage multiple orders and deliveries. Assemble it. Install drivers/configuration specific packages.
All of these things are easier today than ten or twenty years ago - but assigning it to a random mid-level engineer and I'd set my project management gamble on half a day for the busiest, most focused engineers least likely to take the time to fuss over specs, or one day for the majority.
ofc. to get to $1000 for that they'd still have to be on $230k to $460k.
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.
A senior engineer in the Bay can easily pull down $400k/year in total comp, which is $200/hour. The rule of thumb I've always heard is that a fully-loaded engineer costs roughly 2x their comp in taxes/insurance/facilities/etc.
When someone costs the company north of $3k/day, it's cheaper all round to just plonk a brand new $6k MacBook Pro on their desk if they have a hardware issue.