Isn't a blockade of one nations ports by another nation generally agreed to be an act of war?
Simply mobilizing along the borders, but not firing a shot, is EFFECTIVELY starting a war with Israel.
Israel has a far smaller population than the neighboring Arab states, and thus has to mobilize a far higher % of its population for war. The Israelis are unable to mobilize their entire army and keep it mobilized for more than a few weeks, maybe a month, before their entire economy would collapse because there's no work getting done. However, the Arab states can stay mobilized far longer. So, basically, Israel generally HAS to strike first; they can't sit around mobilized forever.
In 1967, technically, the Israelis "started" the war because they fired the first shots; The reality was that they really couldn't do much else.
The Arab states are aware they'll get struck preemptively if they even begin to mobilize in a serious way; hence, they don't do so.