There's trouble, there are troublemakers, no question, but nothing that the army and regime can't handle. The Sinai is still considered a non-Egyptian province, as it was in ancient times, and the jokers doing the terror and killing don't consider themselves Egyptian for the most part. They are financed and armed from outside the country (iow, the Iranians) and cover is at a premium in much of the waterless hellhole that is most of the Sinai, so the terrorists operate in or near the various seafront resorts. They can't really run for it, because there's really nowhere to run.
In the era of asymmetric warfare, you can’t ignore the growing fundamentalist threat across all the Muslim world.
They get to pick the time and the targets while the army comes in to clean up and kill off the crazies afterward—but that doesn’t stop the initial terror event.