Given that the additive(s) that caused the diseases was identified around that same time - Vitamin E and/or CBD oil - maybe Trump recognized that such a total ban was unwarranted.
I don't have a horse in the vaping race and thus haven't followed this super closely, but two facts told me that the problem of the diseases was not vaping generally:
* Vaping, including flavored, has been a "thing" for something like 10 years, maybe more;
* The severe lung diseases started showing up much more recently, perhaps within the past 2-3 years.
IOW, the disease cause was not vaping generally but something that changed 2-3 years ago. Thus, what should be targeted is the specific cause(s), not the whole industry. But power-hungry control-freaks among bureaucrats don't think that way.