Um there are many reasons all of which boil down to money. The deeming is designed so that no one except large tobacco companies can afford the estimated 1500 hours and one million dollars (per SKU) to get there products approved. The large open tank systems and multitude of flavors will all go away. Only the sealed 'cig alikes' will remain. Which are far less effective at helping people quit smoking combustible cigarettes than the larger second and third generation devices.
Second is lost revenue from both direct taxes and the Master Settlement Agreement. Which is a hidden tax that a hand full of states including California spent before they even received it by selling bonds. So many people have quit smoking in recent years that several states are at risk of default on these bonds.
Third is that the rabid anti smoking zealots would be out of a job if the truth was told about how harmless vaping is compared to smoking. The Royal College of Physicians released a report just a week ago which confirms what us mere mortals have been saying for years. At least 95% less harmful, not a gate way, etc.