Jesus claimed to be a king. The Roman’s took that literally. He was given a chance by Pilate to recant, and doubled down.
That’s what he was executed for (Rebellion, inciting insurrection. All that nastiness.)
Sure, his followers took it metaphorically, but he had an opportunity and doubled down on it.
Sure the mainstream jews wanted him dead because he was (in point of fact, yet another) mystic running a cult, and it was stiring up the common sorts enough they were having problems.
The Pharisees would have knifed him and left it at that, But the romans were getting a little irritated with all the dead bodies being left around- untidy that. The Roman’s cracked down on that sort of thing, so they had to have him tried in Roman courts for breaking Roman laws. Pity he made it so easy.