Perhaps you need a better map. Gotland is a prime target for Russians. Establishing air defense batteries on Gotland, along with capturing the Suwalki gap between Poland and Lithuania, are two key steps of invading the Baltics. Suwalki cuts the land supply route and Gotland the air and sea routes.
To prevent liberation of Gotland and keep Swedish armed forces busy, they would then terrorize the remaining parts of Sweden with drones and missile attacks on cities the same way they do in Ukraine. Even Sweden isn't rich enough to buy enough air defense systems for that, hence the need for NATO to get access to pooled resources.
It's a simple calculus.
