If my recollection is correct...it is an OSFI (or maybe federal) imposed requirement that for those working in a capital markets / IB type firm that their own trading accounts be operated under the same umbrella as the employing firm - from a regulator risk management perspective.
If my memory is foggy and it is not imposed directly by the regulators, then it is a good risk management strategy for the firm to use, for when the regulators come knocking and ask the firm to illustrate how they are managing regulatory, economic, capital, market risk.
That requirement seems to have been pretty standard practice through my rotation through the big 5 over the last few years.