Not all the teams have goalie styles available, but there is some gear for almost every team in the world.
While the long sleeves of a goalie jersey may protect the skin, the goalie isn't working any less hard than any other player, and that means that the extra fabric can cause overheating during a long game.
One of the key reasons that a goalie needs a separate-but-complementary jersey is just so that the referee can tell which two players on the whole field are entitled to literally handle the ball.
The goalie is an important position, whether you're watching or playing the game, and deserves not only the right equipment but also the ability to guard their goal in style.
Your team may be trying to budget and be tempted to simply put the goalie in the same jersey or T-shirt that the rest of the team wears.