When a flat-color 3D model looks blocky in details, the main cause is a low polygon count—too few triangles in the mesh to define smooth edges or fine features.
Flat colors (solid, untextured surfaces) don’t mask polygon edges like textures or shading do, so low resolution stands out more. This often happens if the model was exported with too few polygons or over-optimized for performance.
To fix it, increase the polygon count in your 3D software (e.g., subdivide the mesh) before applying flat colors—this adds more triangles to refine details without losing the flat style.