I worked at HP from 2014 to 2021, though not for the Instant Ink team.
The TL;DR is that I think Instant Ink is an absolutely fine program that's ruined by morons that either can't read or think they're devious and think they're going to be able to swindle HP out of ink for pennies.
The first thing you absolutely must know is that Instant Ink is an optional program. You still have the ability to buy and use normal ink cartridges. IMO, that alone should shrug most criticism of the Instant Ink program. You think it's a scam? Fine. Don't subscribe to it. Done.
Second, Instant Ink is not a subscription to ink cartridges, it's a subscription to printed pages. The ink is merely provided as a vehicle to provide the printed pages that you're paying for. That's why the Instant Ink subscription tiers are based on printed pages, and not based on ink used.
This means that if you subscribe to Instant Ink, get your cartridges, then cancel the plan, of course you don't get to keep printing with the cartridges! You didn't pay for the ink!
This is not scumbag behavior. You didn't pay for the ink. You paid for printed pages. You canceled your subscription, your quota ran out, so why would you think you get to keep printing with those cartridges?
But...people think they're geniuses! They rub their hands together while thinking "Heheh, I'll buy a month of Instant Ink, get my cartridges, then cancel, and I'll have received ink for only $3!" then go into an absolute rage against HP when they go through their quota and their printer won't print anymore. It's completely stupid.
If you print frequently and will actually use most of your quota, Instant Ink is a great program that actually does save you money on ink! But people misunderstand (likely deliberately) how it works, and think it's a scam and that HP is a shitty company for it.
It's still HP's fault. It's their business model and people will be people, including the too clever for their own good, irrational skinflints that are prone to raging on line.
Behavior is frequently hard to anticipate, but this isn't one of those cases. If your scheme involves everyone comprehending subscription terms you've failed: people don't do that, for better or worse.
Imagine you buy a can of turtle wax that locks after 20 opens. "We don't sell wax! We sell car waxes!" A water hose that sells sips of water.
You're buying ink. Just because HP wants to market it as something different doesn't make their bullshit true. Unless they're shipping you a printed page, they're selling you ink and then charging you per use, their bottom line doesn't list pages printed, it lists profit per cartridge. People just don't like buying an object and paying for it like it's a service, because it's an obvious scam. Ink is a product.