They can say it is perfectly legal for drug companies to speak, but it is illegal for the TV networks to sell them add time. The TV networks are not engaged in speech when they sell time to advertisers, and they remain free themselves to say whatever they want to say.
It is my undestanding that drug adds are not prohibited by the EO but rather the ads must include the complete list of side effects.
The complete list is considerable and if included in the ad might be so great as to direct attention away from the actual product.
I can not confirm that thought however, I do not recall the source