In the beginning was slotted heads, mainly because mass machining and casting wasn't good enough to have more precise forms. Then came the Great Connector Wars, and in the US the Phillips head won and was standardized; almost every house built in the US in the past 80 years will be built with these (and nails). Slotted heads are much less common, but you find them in various specific places, like where the heads are visible and you want to hide the screw as much as economically possible.

Canada, however, was smarter and standardized on the Robertson head; IIRC one reason for the divergence was the Phillips licensing cost. In any case, Robertson is superior to Phillips in most ways, except it's even worse to dig out if it gets painted over.

As machining improved, many attempts were made to improve on Phillips, which mostly amounted to polishing a turd; Robertson remained unchanged as it was already pretty good.

Then came hex, which is great except it's structurally pretty terrible for the head. Still, it can be seen as an improvement in Robertson, but not quite so good as to be worth all the retooling. Good enough that it's probably the second, or at least third, most popular head in the US.

Finally, someone did some fucking math and came up with Torx, which is provably and demonstrably superior to all other screw heads. It maximizes force transfer, and leaves more material in the head; it's harder to strip out, and can be applied effectively to very small screw heads. There's a security version, which was mostly useless (for intended purpose) the day after it was released, but beyond that, there's no real improvement that can be made.

The Phillips patents expired decades ago, so it's holding on mainly from inertia. Commercial contractors don't have much invested in it, because they have to literally buy boxes of replacement Phillips heads because of how shitty the design is and how often the heads break. While manufacturers have a steady stream of revenue from selling replacement Phillips tools that have broken, this is balanced by the mouth-watering prospect of every contractor in the US buying new Torx size-sets and high-end Torx tools. And the screw makers probably DGAF as they'll sell screws either way; Torx screws might be a little more expensive - they used to be, but I haven't compared lately.

Canada may just motor on using Robertson; there's less incentive for them to retool since Robertson isn't nearly as crappy as Phillips, so the cost/benefit to upgrade to Torx is less compelling. But who knows?