I dont know why they would choose 200m deep, its pretty dark at that depth and not super interesting. Why not park it somewhere near a reef at 30-50M, dive in dive out experience for tourists, good vac options, good lighting and easy to work on.
It’s a cap, not a target. Up to 200m, initially only up to 100m. It’s also for scientists, so the benefits are that you don’t have to keep returning to the surface. The whole idea is to reduce the cost and interruption to the work the scientists want to do. At 50m you can get to the surface fairly easily. 200m much harder.
Think of it like your first subnautica base.