We're talking about different things here. I was talking about building new fabs for 28nm nodes and you're talking about TSMC upgrading existing fabs from older nodes to 28nm production.
Of course upgrading an existing older "sunk-cost" fab to 28nm production will be profitable, but not building a new one from scratch just for that same older node.
But now this makes the subsidies angle make more sense: You subsidize initial construction and then the domestic plant remains online indefinitely because the construction is a sunk cost and the incremental cost of upgrades over time is sustainable.
Of course upgrading an existing older "sunk-cost" fab to 28nm production will be profitable, but not building a new one from scratch just for that same older node.