Why inlets don’t have great collisions

Recently I have started Unity (Unity 2021.2.a11 I believe) and have discovered why you can’t have hollow shapes on the game. So it goes between one of two reasons:
1. Devs decided to use a cylinder collider for easier collisions.
2. As of 2019 Unity stopped allowing “convex” colliders. This would refine the collider and make it follow the true shape of the mesh. Since this is not true anymore the mesh fills in and make it impossible to go through it.