I believe the in-lore explanation is that the teleporter always has to be in the path of any transport. So if going from the bridge to a planet, the teleporter actually teleports you twice: once from the bridge to the teleporter buffer, and next from the buffer to the planet. The room was where the teleporter was physically located.
With improved technology later in the timeline (Discovery), they did in fact abandon the need for the teleporter room altogether.
For what it’s worth, they never did address the most fascinating aspect of teleporters: that in the future they solved the problem of how to transfer consciousness. Though the existence of Thomas Riker does raise issues that are unresolved unless you accept that either teleporters do in fact kill you or consciousness can be copied. Based on how willing people are to step into them, you would imagine it’s not the former.
Why is it being review bombed?