Because only now are viable professional alternatives to Adobe programs starting to show up. Adobe would be shooting themselves in the foot by working with some interoperable plugin format. Also, for graphic design at least, plugins are a much smaller part of your workflow than they are in audio production— the basic tools really are the most important thing in design. I'd say most professional graphic designers, if absolutely necessary, could replace their entire digital workflow with a few hundred dollars in art supplies, maybe minus typesetting and color matching functionality, and likely produce more interesting (if much slower and less polished) results. I don't even think they make Letraset letters anymore.
