The Province wanted a common vehicle that could be operated in any jurisdiction where it was directing Metrolinx to make a transit investment, whether Toronto, Kitchener, Hamilton, or Mississauga.
i.e. Metrolinx 6201 is wearing a TTC badge today but, at its most extreme, if it needed to be transferred to Hamilton tomorrow, it could. Just slap a Hamilton Street Railway logo on it.
Personally, I think that this mentality ( while not flawed, but stretching scenario analysis a bit too much) resulted in Crosstown receiving a vehicle that is technically adequate, but not necessarily the best for its primarily subway service-like role.