Why exporting to STEP or IGES doesn't hand the next engineer an editable copy of your model — it hands them the shape, not the recipe that built it.
A mechanical engineer emails a SolidWorks part to a supplier who runs CATIA, and is surprised when the imported file shows up as a single gray blob they can't edit — no sketches, no extrude, no fillet parameter to bump from 3 mm to 5 mm. Nothing went wrong. That is exactly what a neutral CAD format is supposed to do: carry the finished shapeacross a vendor boundary that has no shared understanding of how either company's CAD kernel builds features. The feature tree — the sequence of sketches, extrudes, fillets, and patterns that make a part editable and parametric — is native-format-only. STEP and IGES were never designed to carry it.
SolidWorks, CATIA, Creo, NX, and Inventor each build a solid using their own internal feature tree structure, their own sketch-solver, and often their own geometric kernel (Parasolid, ACIS, CGM, Granite). None of those vendors agree on how a "fillet feature" should be represented internally, so a format that tried to carry feature history across vendors would need every CAD kernel on earth to agree on a common feature language — which has never happened. STEP and IGES sidestep the problem entirely: instead of describing how the shape was built, they describe only whatthe shape is — a boundary representation (B-rep) made of trimmed surfaces, edges, and vertices that any kernel can rebuild geometrically, without needing to understand the other program's features at all. That is the entire trade being made: give up editable history, gain universal portability.
Neither half of that is right. First, STEP does not preserve design intent in the parametric sense — it preserves the finished geometry, not the sketches, dimensions, or feature order that produced it (some STEP AP242 files can carry PMI/GD&T annotations and semantic assembly structure, which is real progress, but that is still not an editable feature tree). Second, STEP and IGES are not equivalent neutral formats. IGES, standardized in the early 1980s, typically represents a part as a collection of independent trimmed surfaces rather than a single closed solid — surfaces frequently don't meet edge-to-edge with the numerical precision needed to form a watertight body, which is why IGES imports so often need "surface healing" or manual stitching before they behave like a solid at all. STEP (ISO 10303, especially AP203/AP214/AP242) represents a proper B-rep solid with defined topology, which is why it imports far more reliably as one clean, watertight body. For that reason most CAD teams now treat STEP as the default exchange format and IGES as a legacy fallback for old files or old partner systems that predate STEP support.