The three extensions you mentioned would all be busier than Eglinton West. Eglinton East is another thing (especially once you dump half the SRT riders onto it), but the difference for Eglinton West is that there's nothing there. No jobs, no schools, no malls, few large concentrations of people, very little prospects for redevelopment, and maybe, what, 1,500 people per hour now on the bus? There's only so many people that will be diverted from other routes (and of course, no mention is ever made of GO integration for areas like Rexdale) and the 'airport market' is much smaller than it seems. But it's all moot because Eglinton got funded, though the line may never actually reach the airport, anyway.