You often see people describe Jesus as "an obscure Judaean rabbi" or something along those lines, especially if they try to give a more historical accounting of his life. But like... he doesn't really sound much like a rabbi when you read the gospels? Sure he clearly has strong opinions on religion and does seem somewhat knowledgeable in biblical literature (at least if we believe the gospels to accurately transmit what he said.) But I can go to synagogue right now and find ten other people who fit that bill without being rabbis. He never seems to go through training to be one and he disagrees a lot with the pharisees who are the precursors to modern judaisms rabbis.
So like, is there any historic reason that he keeps being called that? Did the word mean something very different back then, which is why some historians use it? Or is it just people assuming rabbi = a Jewish guy who knows a lot about religion?
It's important not to conflate a rabbi from today's definition, which is an institutional title, and the way it would have been used before "rabbinic Judaism." Rabbinic Judaism invented a particular idea about what a "rabbi" was, and it (not unlike Christianity's idea of apostolic succession) had to do with channeling proper interpretation (though there wasn't nearly as closed a view in Judaism, since they didn't quite develop the idea of "heresy" in the same way that Christianity did [see Daniel Boyarin, "The Christian Invention of Judaism: The Theodosian Empire and the Rabbinic Refusal of Religion," Representations, vol 85, no 1, Winter 2004, 21-57]).
Before all this, Jesus could very well have been considered a rabbi simply because he taught stuff and had followers; it really could have just meant "teacher," depending on context. Jesus's disciples could have intended some kind of prophetic meaning here, as Jesus may have also viewed himself as having some kind of prophetic role, gathering disciples for the end times. See John P. Meier, A Marginal Jew: Volume 3 (2001), chapter 25, where Meier discusses the nature of Jesus's relationship with his disciples. Basically, Jesus had disciples, they were considered disciples, and in order for disciples to exist, there must be a leader/teacher, and that's what a rabbi is.