wt's argument is, that Rev 14, (the other text mentioning the 144k is Rev 7), says, that they are the ones that "follow Jesus wherever he goes". he went to heaven, therefore, , so must they.
by contrast the rest of the living do not go where Jesus went, so they must be on Earth.
These earthly folks are the 12 tribes of the Israel of God. confusing? yes wt writers are confused. conveniently.
7, 14, 14 4000, (12x12 000) , all very spiritual numbers in wt numerology, organisational perfection. in contrast,
The great multitude (who no man can number), wt tries anyway reporting tabulating every detail.