This is true. The fear of war is indeed the real reason for Iran's passivity, amidst the regime's likely survival in times of war.
But, as we are seeing, Israel is crossing all the red lines that Iran has verbally declared, with Iran showing all this passivity. The lack of reaction is also dangerous for the Iranian regime, after all, it is increasingly exposing the regime's weaknesses, while it may even consider a civil war if the West sees that Iran is too fragile to react proportionately.
As I said, Iran needs to seriously change its military posture/readiness. The escalation is becoming increasingly aggressive, Israel will not stop and not even the US will contain Israel. The only means of containing Israel would have to be Iran, which is showing all this passivity. Turkey only talks and does nothing, on the contrary, it even helps the Israeli regime. Egypt has many problems and will not face Israel.