So then the culprits are the company’s own engineering and marketing departments for not correctly anticipating user demand.

Sure .. also them.

Having said that, I am usually empathetic to these kinds of 'unlimited' deals because even though they aren't really 'unlimited', they do tend to be generous to the average use-case and average user .. Inevitably, and unfortunately, someone decides to test the limits and the entire thing collapses.

It reminds me of the Blockbuster "No more late fees" policy, which was a really good customer-friendly policy (speaking as someone who regularly returned rentals late) .. but then they were sued because an aspect of the policy had Blockbuster charging the cost of the rental to the customer if it wasn't returned in some period of time .. and because that charge looked like a 'late fee' they got sued. Urgh.

Looked like? Sounds like it was a late fee. Look at us, we've got the cheapest plane tickets by $25 ($50 booking fee applies).

IIRC it wasn't a late fee it was a "you kept it over a month so you have to buy it price."

It’s not any more possible to correctly anticipate all pricing structure vulnerabilities, than it is to correctly anticipate all program and API security vulnerabilities. There is always a statistical chance of novel outcomes when humans are involved.

Or you take your best shot and then adjust as needed.