The lack of competition is the actual reason. When Google was entering markets with their Internet service suddenly incumbents got capacity to provide competitive speed at slightly lower price. Essentially causing Google to give up with that initiative. If a company with "unlimited" amount of money like Google can't enter to compete, no one can.

And if there is no competition, you no longer charge competitive prices, you charge what people are willing to pay. The whole promotional plans they offer are used to figure out how much you are likely to pay. Once the promotion expires and you don't call to get it extended, you are basically saying that you're ok with increase. Once enough people don't do that, the price will go up.

Similarly, here in Canada, after Bell's UBB plan (forcing TPIAs to the same restrictive 25GB cap as the telcos) fell through, they wasted no time coming up with unlimited plans.

Having lived in a couple of developing Asian countries, there’s a few obvious reasons that the services would be cheaper. For starters, everything about doing business is cheaper, especially salaries. Unreliable service is completely normal. There’s also additional income streams for service providers. Getting spam SMS tailored to your nearest cell tower (like special offers for nearby restaurants) is completely normal. HTTP content is much more common place, and it all has ISP injected advertisements. Service coverage is also much worse, tourist areas have the best coverage, followed by business districts.

That may be the case for some countries but it doesn't really explain the difference between the US/Canada and Europe or Australia.

If you looked into comparing the services from any two different countries, you’ll find completely different sets of market and geographical circumstances. The costs of providing the service will be different, the actual service provided will be different, and the demand from consumers will be different.

If you compare Australia and New Zealand for instance, there’s some very obvious factors that could explain that difference. Australia has a lot more outbound submarine bandwidth than New Zealand has, with New Zealand also being much further away from the rest of the world. Most of Australia has either no service or terrible service. New Zealand has approx the population of Sydney, while having more than 20x the land area. Australia has about 5x the population of New Zealand, so all of your fixed prices per customer are going to be less in Australia.

For any two countries you’re going to get an incredibly long list of factors that influence price. Population density seems like it should have a significant impact on the cost of building and maintaining mobile infrastructure for example. The US has close to 10x the population density of Canada, and Europe has over 3x the population density of the US, which I would expect is a non-trivial contributor to the reason that Canada is more expensive than the US, which is more expensive than Europe.

I think the price of mobile data in Australia well and truly puts to rest the "US is big" argument.

Also I'd say puts to rest arguments about wages/regulation being the issue.