There is too much critical infrastructure that relies on the Internet, and I'm not talking about Government stuff, I mean water utilities, electric utilities, gas utilities, finance, and not their SCADA systems, but their ERP systems, finance systems, etc. Almost all B to B commerce runs across the Internet. I'm sure there are still some hold over dinosaurs, but most things traverse the Internet.
Trump is doing everything he can to placate big business and the stock market. If he were to turn off the Internet he would stop almost all U.S. Businesses, it would be like driving into a 30 ft thick concrete wall at 180 MPH.
Turning off the Internet would also cause a public panic of epic proportions, taking a bad situation and making it so much worse.