That is because the CRTC (Canada's equivalent of the FCC) doesn't have the network non-duplication and syndicated exception rules that the FCC has and those same laws which the US Congress passed and President signed into law. It is those rules which created compliant feeds of WGN and WTBS, which the Canadians never had to follow. So, they still get the local channel.
A bit different than that actually.
The CRTC has different rules about getting approval to show American "cable" channels and "OTA" channels. And the royalties are different as well. Cable channels need to be negociated, and shown to not be to the detriment of Canadian cable channels, OTA channels have a very minor royalty payment, and don't need the channels approval to be shown. They also don't fall into the requirement of not repeating another Canadian channel (SimSub requirements not withstanding). Only the OTA versions were ever approved for carriage in Canada, the cable versions weren't. And since the OTA versions were cheaper to carry, the providers never had a reason to pursue approval of the cable versions.
As for network non-duplication (neither was ever legally considered a network affiliate) and syndicated exceptions, neither WGN or WTBS really fell into that. In WTBS's case, all it's programming was cleared nationally, the reason for different feeds was for differing commercials (local vs. national) and local Educational/News requirements.
WGN similarly cleared most of it's programming nationally, but a couple years after the WB started, decided to remove WB programming from the national feed in order not to draw viewers away from other WB affiliates (WB never achieved network status, per law, so network exclusivity never entered the equation, especially since Tribune owned most of the WB affiliates anyway).