IGES and STEP files to STL conversion issue

Im using these two code snippets to convert IGES and STEP files to STL file.

IGES to STL :

IGESControl_Reader reader;
reader.ReadFile(file_in_occ);
cout << "IGES File loaded" << endl;
Handle(TColStd_HSequenceOfTransient) myList = reader.GiveList("iges-faces");
myList->Length();
reader.TransferRoots();
sh = reader.OneShape();

BRepMesh_IncrementalMesh aMesh(sh, 0.1);
sh = aMesh.Shape();

StlAPI_Writer myStlWriter;
myStlWriter.ASCIIMode() = Standard_True;
myStlWriter.Write(sh, file_out_occ);

STEP to STL :

STEPControl_Reader reader;
reader.ReadFile(file_in_occ);
cout << "STEP File loaded" << endl;
reader.TransferRoots();
sh = reader.OneShape();

BRepMesh_IncrementalMesh aMesh(sh, 0.1);
sh = aMesh.Shape();

StlAPI_Writer myStlWriter;
myStlWriter.ASCIIMode() = Standard_True;
myStlWriter.Write(sh, file_out_occ);

The problem here is, for some files, conversion takes a long time and the file size sometimes go close to a GB. Im attaching such a file here.

But when I convert this same file using ImportExport application built from the given sample, the file size is just within 200kb. I expect an output similar to the one from ImportExport application.

Where have I gone wrong. Can someone please guide me to get the expected output.

Thank you