They also exploded Dr. Kananga in LALD, and Mr. Kidd gets set on fire in DAF. What we see when Killifer gets eaten by the shark isn't really any more graphic than when Helga Brandt got fed to the piranhas in YOLT or Stromberg's secretary got fed to a shark in TSWLM. That said, the level/quantity of violence and (perhaps) the cold-bloodedness of it was enough to make LTK the first PG-13 rated Bond film, but maybe apart from Dario getting fed to the grinder, it wasn't anything we hadn't seen before.
My understanding was that Krest in the decompression tank was the main point of contention. Kananga blowing up in LaLD was bloodless, Krest was far more graphic. I'd argue Mr Kidd being set on fire in DAF is far less brutal than Sanchez's end, and frankly is almost played for laughs so I do think the cold bloodedness of it was a factor, even before you factor in Felix getting his leg chomped off and Della's presumed rape and murder

As an aside it always amuses me how similar Anthony Zerbe's deaths were in LTK and Star Trek: Insurrection
