Point #1
As I understand this decision is not from the White House or Trump but from the people who are experts in these areas and advise the President.
Trump as I understand it in fact wants the ventilators to be produced.
Point #2
Technical/Technological Decision
Point #3
Supply chain and risk mitigation decision
nytimes: it seemed clear to several officials that the agency would have to select multiple manufacturers, in part to avoid the risk that one production line runs into technical troubles, or that its workers contract the very virus the ventilators are being built to defeat.
Point #4
Highlighted below are experts who know more about this than my guess is any of us here do.
nytimes: Targets have changed by the hour, officials said, as the Centers for Disease Control and Prevention, the Department of Health and Human Services, the Food and Drug Administration, which approves the use of medical devices, and the White House try to figure out how many ventilators to request and how much they should cost.