>>712704389Because the other handful of websites are already echo chambers where the algorithm/mods propagate what they want and silence what they don't like. For a price.
But the structure of 4chan requires a more "hands on" approach to advertisement, so they pay the mods to look the other way when they flood the catalog with the same cookie cutter threads with the same cookie cutter replies fellating the product. And when you point it out they dogpile and call you a schizo/tendie/snoy/poorfag/incel/barrydraconirian/whatever.