There are all kinds of people on this planet, from all kinds of backgrounds, and everyone's different.
Some are rich, some are poor, some are healthy, some are very sick, some are intelligent, some are very dumb, some are oung some are very old.
When you put all this together, isn't it unreasonable to expect everyone to become JW's, or everyone to become Catholic, or everyone to become Muslim?
I'm sure that even if everyone wanted to become JW's it would be impossible.