Many of the above comments are spot on. I’ll just add sometimes becoming a T/A can be a good "in " into the department. My S made friends with many of the PHD students in the CS department during office hours through his T/A work. One in turn brought him on board an A/I research project. The professor in charge did not even look at his resume or grades when he interviewed him even though they were quite strong. He only cared that the PHD student was vouching for him, that my S was pleasant and was willing self study the foundational A/I course over winter break. Friendship pays. From this he will be involved in two research papers. People that like you help you.
The other point is more opportunities typically come when you are an upper classman. There may be an assumption that non upper classman do know enough yet to be useful. The first time my S was offered an unsolicited research position was the start of his senior year. By this time he was too busy doing other projects to accept it.