One of the companies (let's call is "Bell") owns a national fibre network, the last mile of copper or fiber to the home, ISP service, mobile phone service, and several national content networks. It receives significant subsidies from the federal government for providing national backbone service, fixed wireless service in rural areas from its extensive network of towers, and content production on its networks. The other duopolist is similar, but started in the cable TV business instead of the telephone business.
These duopolists are required by law to allow third-party ISPs to use their backhauls and last-miles in exchange for some of the government subsidies. They do this grudgingly, using loopholes like providing twisted copper pairs to the third-party offices even when fibre passes outside their door. Regulations allow (and there is plenty of admission of, and lawsuits over) deep packet inspection to allow "traffic shaping" based on content and connection. At one point the cable company was successfully sued because they throttled all encrypted traffic on the assumption that it was VPN streaming pirated video content in competition with their own service., causing gaming to be useless for half the country.
I understand these are first-world problems. I own shared of some of these companies, and they pay good dividends. It doesn't mean they are not unethical.