It works for you because you print a lot (1-3 pages per day!). OP prints fewer than 10 pages per year.
The author would pay $12/year for 10 pages per year, without the cost of the cartridge. You need 20 years before you reach the cost of a $240 cartridge. The cartridge would’ve dried out before then.
This entire article is an exercise in “I can’t do math”
More directly to your point - the author plainly acknowledges the sunk cost fallacy at play here. I’m pretty sure he can do the math.
Anyways, he plainly acknowledges the sunk cost fallacy at play here.