likely the same way as during the last 30 years: If enough "big players" move to a new social network, their peer groups will also move.
Main problem for marketing in the Fediverse:
no amplifying algorithms
no ads you can buy
And we like to talk and discuss a lot, and perhaps you can sell a thing you create, because people are interested, but "BUY MY SHINY PRODUCT" doesn't work well.