The unexciting real answer...
Canadian here! They are just a throwback to when bottles of maple syrup were larger and made of earthenware pottery. It’s really just nostalgic. Plus if you heat your maple syrup in the bottle, you can use a kebab stick or whatever to haul it out of the hot water by the handle.
Otherwise known as a ‘skeuomorph’.
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A skeuomorph is a derivative object that retains ornamental design cues (attributes) from structures that were necessary in the original.
I always figured it was for a lanyard holster system so if you’re chugging it in a tight spot and drop it would just swing down your leg instead of hitting the ground and shattering