There is no "Ban"... There is an investigation into certain foreign manufactures. The investigation, as of yet, involves the holding and restriction of certain devices and chemicals.
These devices are being held, due to the advertising which identifies them as a smoking device. (Though they are not a "Smoke" delivery device.) In the USA, smoking devices need to be registered, for control of sale from minors.
These liquids, which contain a "Known poison", and "Known regulated substance", being lethal levels or quantities of nicotine and
tobacco extracts, may be subject to
tobacco control, and may be subject to poison control. (Some require special package notifications for shipping and handling. Some require registration with the tobacco departments for importation. Being a regulated "Plant" derivative.)
Lack of labels, ingredients, lot numbers, ownership, and the abundance of counterfeit items rolling into the USA, has forced this investigation. Pressure from ruyan, for failure to enforce their patents, by allowing knock-offs to enter the country, has also played a role. Ruyan has begun legal pursuit of all the knock-offs, such as "E-cig", the company.
Release of unknown chemicals, whose contents are not defined, and whose instruction indicates consumption, is within the rights of the FDA. It does not have to be a tobacco item, it only has to be an unmarked consumable. The devices are out of the FDA's control, but are a counterpart of the liquid, as the liquid is within many of the devices.
All large packages, from certain suppliers, are being forwarded to an investigation storage area, and others are being returned to the sender.
The removal of questionable devices from sale, is not a ban, it is a safety precaution. A "Ban", would be a publicized and permanent resolution that would require legal change, to reverse. The FDA has not yet made a determination, other than listing these items as, "Items of concern, for immediate temporary removal, pending the outcome of a legal investigation."
Short answer... It is sellers and consumers calling it a "Ban", not an FDA declared "Ban". (This is a perceptive view, not a politically correct fact.)