[Cronos]

Actually, Hadrian did start off as a "friend" of the Jews (there was no "Israel" and hadn't been one for 800 years).

The two main reasons for the revolt were
1. the aftermath of the KITOS war (the 2nd Jewish-Roman war from 115 to 117 AD) - when Jewish fanatics massacred gentiles in Cyprus and Cyrene (they completed killed off everyone in Cyrene)

2. Hadrian rebuilding Jerusalem -- Jerusalem was destroyed in 70 AD, the temple burnt to the ground (as Jesus prophesied in the Olivet discourse in Matthew and Luke)

Interestingly - during the Bar Khokbha revolt -> the kingdom of Israel was re-established but temporarily

Blue is the restored Israel -- the era of the redemption of Israel was announced, contracts were signed and a large quantity of Bar Kokhba Revolt coinage was struck over foreign coins.

Note that Simon Bar Kochkba was considered the Jewish Messiah, hence his "bar Kochkba" i.e. "son of the Star" or "Son of God"

[SunkenCiv]

Hadrian was a pedophile (after his catamite Antinoos died in the Nile, he had a city built at the site named after him, had him 'deified', and set up places of worship all over the Roman Empire), and despised the Jews in part because he considered circumcision to be self-mutilation. Throughout his reign he showed that he backed pagan Hellenism and supported the destruction of Judaism.