It's that the rhetoric coming from Trump which, through significant threats to the on-going employment of anyone deemed to be not enthusiastically complying with these daily-updated mandates, increases the likelihood of un-justified "bad thing" happening upon attempting to cross the border to the US.

Basically, the current regime makes it unpredictable, which increases risk. Increased risk = decreased likelihood of related action.

I'm not sure how far off topic we've gone, but "Canadian Devs backing out of attending GDC" would also have a protest aspect to it due to DJT's belligerence towards Canada.