Well, it looks to be yet another relic of alternate "plus 15" urban planning, along with the City Hall walkways, the 181 Uni/150 York/Hilton podium, the upper FCP level, etc.
Probably a victim of the collapse of Metro Centre--and if it were to plug into a retained Union Station, it surely would have been regarded as a disfiguring urban eyesore and blemish. (As it stands, anyway, traffic's surprisingly calm on this stretch of Front, and the median helps from a ped POV...)