Think of the abundance of spiritual food available today, free of charge, in more than 900 languages! It is undeniable evidence of divine backing.
They are constantly looking for ways to validate themselves or prove their own credibility. If they were sure of their claim to be the one true religion, they wouldn't even think about it unless someone else asked them for some sort of proof.
Satan and his world have done much to make the work of that faithful slave challenging, even impossible, to carry out from a human standpoint.
To say that Satan and his world have made it impossible to carry out their "work" is to say that Jehovah's Holy Spirit isn't powerful enough to overcome Satans obstacles.
Satan never prevented them from taking out televised advertisements or infomercials that within seconds would help people around the globe understand their message so that when it was delivered to their doors by local JW's, they wouldn't be blind sided when they showed up. Instead they choose the ploddingly slow method of driving around in air conditioned mini vans and knocking on the doors of empty houses and occasionally when there is someone home, they have no idea what the JW's are talking about.