Beth, thanks for what you are trying to do. I like the MTH 2 rail steam and diesel locomotives and I have bought several during the past year. I don't want to convert to DCC since that is an unnecessary expense when I already have DCS and Legacy and neither is compatible with DCC (unless running Proto 3 locomotives in DCC mode). I think MTH got it right when they introduced the 3-2 convertible trucks. For diesel locomotives, there are not that many different parts (pilots, wheelsets, handrails, couplers) that are required to manufacture 2 and 3 rail versions. For steam, many of the latest MTH premier locomotives are electrically equipped to run either 2 or 3 rail, so all that is generally is required is to manufacture versions with scale wheelsets and (potentially as a bonus) to provide a shorter drawbar.
For me, these locomotives are adequate. It would be nice to have two sets of screw holes in the 3-2 trucks to move the truck side frames inwards for 2 rail operation and a variety of other improvements, but it's better than having to wait decades for a specialty manufacturer to consider producing something I am looking for now. Also, offering undecorated versions would allow modelers to customize for the more obscure railroads or for railroads that are not commonly represented, such as Illinois Central.