Gallant is a highly experienced military official and has shown a strong track record that demonstrates the necessity of his position in Israel's security establishment. Given the fact that the war is still ongoing, firing Gallant at such a decisive time in the conflict could be disastrous.
Gallant has lost much legitimacy in the eyes of those in his own party due to his constant undermining of Israel's negotiating position. Though nothing is certain as of yet, Netanyahu is well within his right to sack Gallant over his incessant attacks on Israel's strategy to free hostages and destroy Hamas.
Gallant is a war criminal guilty of genocide due to his involvement in Israel's war on Gaza, and a new defense minister would have a marginal impact on the brutality under which Palestinians live. Indeed, Netanyahu wants an even more aggressive figure to take the role of defense minister.