You are right, and i think that air drop will rather increase even 2019 because companies see air drop as a means of passing information to the general public about their project and the need to invest on them.
Again, Air drop is just another way of distributing cryptocurrency tokens to help with the process of adoption for the particular token. Some ICO projects choose to give out their tokens practically for free to members of their community as a means of encouraging the token’s adoption and usage with the hope that in the process, there will be increased demand for the token which will in turn help to drive up its value.