All meshes are essentially points in 3D space (aka vertices). The 3D program's code "makes up" the rest from these points (and further info, such as light, tex, etc.) Morphs are information on position changes for some, or all, of the points in a model. Hence, they are inextricably linked to the points they're supposed to move, i.e. the mesh for which they were made. Since the points/vertices in a clothes model are usually not the same as those of the figure, the morphs can't be transferred "raw". Tailor calculates from the figure morphs what position changes are needed for the clothing's points to match the figure's morphs. So, unless clothing has been made specifically for the character (such as AMG), you need Tailor to "clone" the character morphs to the clothing. The creators usually put information in their product descriptions about which morphs are available in the clothing - check out the products here in the RMP or on DAZ for examples.