Why did Toronto spend $4 billion on a streetcar?

After six years of construction and with a price tag just under four billion dollars, Toronto opened their newest "subway" line, the Finch West LRT. But at a glance, this line looks more like a tram or a streetcar than a part of the subway network, as the city has classified it. So why did Toronto spend billions of dollars to build a streetcar, and more importantly, was it worth it?