Why did the Jews of Paul’s day reject his claim about Jesus being the promised messiah?

I read from ‘The Triumph of Christianity: How a Forbidden Religion Swept the World’ by Bart D. Ehrman https://www.amazon.co.uk/Triumph-Christianity-Forbidden-Religion-Swept/dp/1786073013

Throughout history, when Christians have pointed to “predictions of Jesus” in the Old Testament, Jews have denied the passages involve messianic prophecies. Christians have long maintained, for example, that the ancient prophet Isaiah was looking ahead to Jesus when he declared, centuries before the crucifixion: “He was wounded for our transgressions, he was bruised for our iniquities, the chastisement for our peace was upon him, and by his wounds we were healed” (Isaiah 53: 5-6). In response, Jewish readers have pointed out that Isaiah never indicates he is referring to a messiah figure. On the contrary he speaks of someone who has ALREADY suffered, and he does not call that one the messiah. More than that, earlier in his account he explicitly indicates who this “suffering servant of the Lord” is. It is the nation of Israel itself, which has suffered because of the sins of the people (see Isaiah 49:3).

source