I'm seeing a lot of replies along the lines of "what does Canada have to offer me as a US tech worker?".

I gather from the tone and from the fact that this is even being asked that these people are US-born, or at the very least have had some easy path to permanent residency.

The linked article clearly explains that this is aimed at H1-B workers in the US, and it goes into plenty of detail about what Canada is offering them that the US isn't.