1) They had to cut down on the amount of blood shown in order to meet MPAA regulations.
2) The trailers were cut by different people. One decided to include more gore while the other went for something more subdued. What makes this theory even more plausible is that the tone of the international trailer is noticeably different than the US trailer. The International Trailer incorporates more of Tarantino’s signature style (including over-the-top violence) and feels more like a Tarantino film.
Image found via Reddit.