First, I think the point should be made that we can reasonably compare the depiction of violence in these films, yes, but we can't reasonably compare the cultures which produced the films based only on these two isolated examples.
There are now (and always have been) varying degrees of gore in film. There are different kinds of violence depicted within every era of film. It's true that from generation to generation the norms shift, but we can hardly say that there was once one way to depict violence and now there is another way. There have always been various temperments on display in film and thus various treatments of violence.
Though graphic violence is certainly more commonplace on screen today than it once was, there are still many, many films that deal with violent subjects yet refrain from gore, blood, and guts, focusing instead on suspense and emotional or narrative content. For this reason we would be amiss to claim that film has categorically become more graphically violent.
If the question we are addressing here is "Why is graphic violence more commonplace today than it once was?" then we can also ask "Who is behind this change, the audience or the filmmakers?"