As others have commented the limit is there deliberately.
Rendering meshes is significantly more expensive that the normal world voxels. (They’re higher fidelity, they’re often animated, they sometimes have VFX, etc.)
Players often comment - that the game runs great until they enter the Therka market. The Therka market is full of entities (and hence meshes). Which simply makes the game more expensive to render. Apart from this, there is nothing particularly special about the Therka market.
Originally there was no limit to what could be placed. Someone could think it was super funny to fill a chunk with huge numbers of meshes. This could significantly reduce the rendering performance for everyone in the area. (An accidental or deliberate way of ruining the experience for other players - aka griefing.)
We looked at every world chunk in the game and set the mesh limit higher than anything that already existed.
This was introduced to protect the community from a bad experience. We also decided to do it, before we introduce many new meshes for the new doors, fences, poles, beams, etc.
With the limit we have some control over the performance and experience for all players.
This is WHY we added it.
However the good news is that as we spend more time optimising the engine, reducing the cost of rendering dispatch, and add more sophisticated LOD then we will be able to increase the limits.
But I should be clear that ideally there would be no limit. The sandbox should allow whatever players wanted.