They probably didn't want to waste ad money on a movie they knew was gonna flop. The money they expected to make with this wasn't from sales at the box office, but rather from financial contributions from China.

Same thing happens in real estate. Americans work with Chinese investors on a real estate deal. Buy lots of land. Promise to build lots of houses. Pay themselves 6 or 7 figures per year to work on the project. Ultimately, however, nothing sells. Few or no homes are built and the Chinese investors are left with nothing, while the Americans putting the deal together are millions richer for it.