Why did Egyptian legions proclaim Vespasian emperor in 69 CE?

The proclamation of Vespasian as emperor by the Egyptian legions on July 1, 69 CE, was not a spontaneous event but rather the result of a contrived plot.12

Following the death of the emperor Galba and the subsequent civil war between rival claimants Otho and Vitellius, Vespasian—then the commander in Judaea—began to consolidate support. While Vespasian later claimed his accession was a necessary response to the misgovernment of Vitellius, the timing and coordination of the military support he received suggest the move was carefully planned.32

After the Egyptian legions declared their support, they were quickly followed by the legions in Syria and Judaea. This strategic move allowed Vespasian to secure his base of power, notably by traveling to Alexandria and controlling Rome's vital corn supply, which helped him exert pressure on the capital while his forces moved to defeat the Vitellian armies.2