Plenty of flippers do be construction as well these days. They'll contract out the foundation and framing, then convince themselves that building the rest is "just a really deep refurb" and end up way over their head.

But lots of national "housing developers" are just as guilty. D.R.Horton (Dr. Whore-tons, as some call them for their propensity to underbid an RFP on development projects then smooth over every delivery issue and run over budget every step of the way) comes to mind for the fact that they can't seem to keep a consistent team of builders project to project even within the same development, where you'll find bent flashings, half as many securements on things like outdoor conduit as what should be used, gutters that would only make the S&WB proud with their ability to drain effectively, and of course the cheapest wood, drywall, sockets, insulation, and other materials they can buy in a different state and transport over.