I definitely know, having been one for 30 years, and also visiting numeral kingdom halls, branches in several countries. However, I am somewhat surprised in a way that they would expect a non-witness with no previous connection (on the most part) to go to an assembly 15 hours drive away... But, it is not the main reason I guess.
It is to keep the Jws busy as well as making them visible in their neighborhoods making known their activities and arrangements.
Also refreshing to see a picture of two pioneers that are not styled the way they are in the JW literature.