So the counterargument would be that shopify realizes it will become a horrible platform if it moves towards the 'higher margin markets'. And therefore doesn't.
Maybe they are looking at the long term. I doubt it, and even if they do so today, tomorrows VC or hedgefund may change this. Still. It is not unthinkable.
I think it's definitely a nice thought, that they'd choose that path, even as their growth slows and shareholders get irate as their market cap implodes (it's impossible to support a $129 billion market cap with their existing business model, they'll be lucky to support 1/3 or 1/4 that). Canada always has an outsized bubble stock with each great bubble; for the dotcom bubble it was Nortel; for the real-estate bubble era it was BlackBerry/RIM; for this one, it's Shopify.
My brain wants to think: hey, the Canadian market might be different, they'll act different. And that sounds great, except by the time this is a critical issue (by the time their current business model runs out of its high growth), there will be immense outside influence over the company and the inside owners and their control will have eroded. As that market cap plunges toward a more realistic fair value and growth slows, the calls for change will be extremely loud. They probably have no choice in the end, they'll need to maximize their position at the center of all of those stores, as the platform so many stores depend on, and that will mean forcing an ad network at the center of it all that they try to milk for margin.
And in terms of supporting that silly bubble market cap, when Amazon was worth just a bit more than Shopify is today, back in mid 2014 (when interest rates were sitting at 0% also), they had ~$80 billion in sales, 27 times larger than Shopify is today. Shopify is either going to crash, go sideways for many years, or they better find billions in profit asap.
Maybe they are looking at the long term. I doubt it, and even if they do so today, tomorrows VC or hedgefund may change this. Still. It is not unthinkable.