Mobx observer doesn't trigger a re-render in React

Question

I am new to mobx and trying to create a simple project that displays a list of NBA players' info using mobx-state-tree.

The fetchPlayers() method in useEffect successfully gets the information and but never triggered a re-render. Is it possible that I use observer in a wrong way?

App.js

import { useEffect } from "react";
import { createList } from "./mst/createList";
import { observer } from "mobx-react-lite";
import { values } from "mobx"

function App() {
    const playerListStore = createList();

    useEffect(() => {
        playerListStore.fetchPlayers();
    }, [playerListStore]);

    console.log(playerListStore.players);
    
    return (
        <div className="App">
            <h1>NBA Players</h1>
            <ul>
                {values(playerListStore.players).map((player, index) => (
                    <li key={index}>
                        <p>{player.firstName}</p>
                    </li>
                ))}
            </ul>
        </div>
    )
}

export default observer(App);

store.js

import { types } from "mobx-state-tree"

const URL = "https://www.balldontlie.io/api/v1/players"

const fetchData = async () => {
    const response = await fetch(URL);
    return response.json();
}

const PlayerModel = types.model("PlayerModel", {
    firstName: types.optional(types.string, "null"),
    lastName: types.optional(types.string, "null"),
    position: types.optional(types.string, "null"),
    team: types.optional(types.string, "null")
});

export const PlayerListModel = types.model("PlayerListModel", {
        players: types.array(PlayerModel)
    })
    .actions(self => ({
        setPlayers(newPlayers) {
            self.players = newPlayers
        },
        async fetchPlayers() {
            const data = await fetchData();
            const newPlayers = data.data.map((player) => ({
                firstName: player.first_name,
                lastName: player.last_name,
                position: player.position,
                team: player.team.name
            }));
            self.setPlayers(newPlayers);
        }
}));

Any help will be appreciated.