You forget that in 1948 Israel had just declared independence. It was expected to capitulate during the war, and the fact it won at all is stunning! Yet even so they lost 1% of the new state's population.

This war was when the Jews lost control of the holy sites in Jerusalem - most notably the western (AKA Wailing) wall.

This new state which had somehow held off overwhelming odds, lost critical territories and suffered so. Simply neither had the ability nor the will to turn towards Gaza (not as significant in any way) before the ceasefire came into effect.

That said, there was one waterfront the Israelis wanted; Eilat. Eilat is at the very bottom tip of Israel and has access to the red sea, so acquiring this would give Israel a second way to open water and open further to maritime trade. After the date of the ceasefire was set a group of soldiers drove down as fast as they could towards Eilat (through the Negev desert) and managed to get there in time. However they had no flag to raise so hastily took a white sheet and with blue ink drew two stripes and the star of David and raised it to claim Eilat and part of the Red Sea coast. 'The Ink Flag' has become a bit of a legend of its own.

TL/DR: Didn't have the manpower to spare and more important sites to take.

Two points to make here. One is that the bulk of the Egyptian Army's expedition force was concentrated in Gaza, from which they had tried and failed to conquer Israel's coastal plain. Israel's counterattack, Operation Horev, aimed at encircling and trapping the Egyptian Army in the Gaza Strip via invading Sinai. Israeli forces reached El Arish on the northern Sinai coast before heavy political pressure from Britain, which had a treaty agreement to defend Egypt from invasion and already was engaged in air skirmishes with the IDF, forced an Armistice. It's pretty safe to think of Egypt as a client state of the British Empire during this period and indeed up to the Suez Crisis.

Without foreign intervention, it's quite probable that the Egyptian Army would have been trapped and forced to surrender.

Point 2 to keep in mind is that the Gaza Strip at the time was already home to 200,000 Arabs, many of whom were refugees from areas already taken by the IDF. Conquering them would have more than doubled the Arab population of the new state of Israel, which in 1949 was approximately 160,000. Many of these refugees would have ubdoubtedly wanted to return to their old homes in the rest of what became Israel. This is perhaps a moot point since Israel never did conquer Gaza but is something to keep in mind when you contemplate how fortunate Israel might have been to take Gaza.