You know what? I'm actually going to agree with you on that. Here are my reasons:
1. Sheppard shouldn't be a high priority for transit expansion of any kind. It really is just a local road (in a regional context), that stimulates local, intra-city travel patterns.
2. If you justify transit expansion on real estate development terms, Sheppard is a sinking ship. There isn't much demand for condo construction on Sheppard Avenue East, because Scarborough is a declining blue collar suburb of yesteryear that isn't highly desired or where people want to create professional jobs. It isn't exactly Flint, Michigan, but investing in rapid transit in Mississauga, Vaughan or especially downtown Toronto is going to give you a much bigger 'bang for the buck' than investing on Sheppard.
3. Hurontario could probably support more trips than rapid transit along Sheppard. Moreover, Mississauga is pretty clear what it wants: LRT, and isn't going to start a political pissing match.
4. The Liberals really need to lock their support in the immigrant, upper middle class western 905. This part of the region is growing in both population and importance; the same cannot be said about Scarborough.
5. It's time to stick it to Rob Ford.