Because it was a deal he made with the province to bury what was already planned for the surface section and then following the Scarborough RT guideway to Scarborough Town Centre to make it one seamless grade separated line. To build the west tunnels and configure it with the Scarborough RT guideway with subway cars would have required a whole new study, design, delays, and probability of being cancelled. He tried to improve what was already on the books even though it wasn't an ideal scenario to begin with due to the initial Transit City plan. We also wouldn't have needed the Scarborough Subway if he had his way with this plan, we would have actually saved money.