Any more streamline than that is apparently more costly or otherwise unappealing to people. It isn’t not small businesses building most homes in the US, they are large, and sometimes publicly traded businesses.
your 100 day house has slack built in so if one crew is running late the next isn't affected. This means you can tightly schedule the labor a month in advance.
There is no slack, because each team has to be operating in lockstep so work never stops, otherwise margins tank and a profitable project becomes a loss.
The expertise of managing and executing this non trivial task is why those businesses succeed, and why landowners outsource development to them.
SFH is itself a waste of money. And land, which is especially expensive where housing costs are high. For every small house different crews need to go there, prepare the site, do the foundation, etc.
Half of the hard costs is labor. (Which is, again, usually high in areas with high housing costs.)
https://www.construction-physics.com/p/what-makes-housing-so...
And of course the opportunity cost due to lost density effect is substantial, blablabla.
The tragedy is that there's a huge discontinuity here, and overcoming that would require a lot of capital (social, political, financial).
And in general construction productivity is extremely meh, to phrase it politely.
https://www.mckinsey.com/capabilities/operations/our-insight...