We might be using different definitions. I'm thinking of the cost of duplicating all the hardware (lines and facilities). It doesn't make sense - one set is enough in a given area, just like having only one set of water pipes, sewer pipes, hydro lines, etc. The nation is divided among the ILECs (fewer actual companies now, since the demise of Stentor), but each company is close to being a market monopoly in its area and would be closer if not for rules governing contracted use. No competitor seriously entertains the thought of building its own competing infrastructure on someone else's incumbency turf; it is self-evident that just the cost of continually upgrading hardware preoccupies everyone involved. Consumers' interests are better served by this (they'd otherwise be paying for much more redundant hardware than otherwise, and there'd be less funding available for private/public expansion into the markets which, charitably, are not profitable). If any of the companies could cut the legs out from under a competitor on its own turf using regulated prices to access the latter's hardware, it would already be doing so.
I can't remember the exact numbers, but back when the federal government was promising Canadians to lean on the telcos to cut 25% off some plans, some wag noted that fees the government charges and requires the telcos to collect on its behalf (and which ignorant consumers probably think is money going to the companies) come close to that amount.
I suspect that if foreign investors were given greater freedom, some with big pockets would swoop in, make handsome offers to current shareholders, and we'd still functionally have 3 large entities with different ownership.