Originally Posted by aliasfox

That's a level of configuration that no shop will want to deal with. My last experience working in bike shops was back in high school/college, but I can't imagine it's that different these days: A bike shows up at the shop nearly complete, and any shop hand can throw the wheels/bars/post on, tune the brakes/derailleurs, and check for major issues (wheel trueness, crank/headset assembly), and get the bike from box to floor in about an hour - often less for an experienced mechanic.

Getting to the level of detail of having a shop build up every half-nice frameset with any component you'd like would turn this from a 30-60 min process to a whole day affair, not to mention the supply chain/logistical nightmare that would bring.

"No, I don't want an Allez with 105, I want the base Allez frame with DuraAce Di2, the saddle off of a Stumpjumper, the flexy post off of a Roubaix, an 11-42 XT cassette, and Turbo Cottons on the Rovals off of a Venge."

"Sorry sir, we can't even run a DuraAce Di2 with an XT 11-42 cassette"

And that'll be the difficulty at that point. That's probably taking it to the extreme, but the industry has to have guardrails in place to keep things moving smoothly. There are far fewer customers who will grumble about the saddle being wrong or the gear ratios being off than customers who will get frustrated because they have to pick something aside from standover height, reach, price, and color. And for the few of us that are really picky, going the frameset route is always an option.