The human brain is stupid and remarkably exploitable. Just a teensy little bit of information hiding can illicit strange and self-destructive behavior from people.
You aren't cut off until you're cut off, then it's over completely. That's scary, because there's no recourse. So people are going to try to avoid that as much as possible. Since they don't know how much they're using, they're naturally going to err on the side of caution - paying for more than they need.
If I sit down for dinner at an all-you-can-eat buffet, I get to decide how much I’m having for dinner. I don’t mind if they don’t let me take leftovers, as it is already understood that they mean as much as I can eat in one sitting.
If they don’t want folks to take advantage of an advertised offer, then they should change their sales pitch. It’s explicitly not gaming any system to use what you’re paying for in full. That’s your right and privilege as that’s the bill of goods you bought and were sold.
I also find it hard to believe 5% of customers are doing that, though.
The dark pattern isn’t the usage limit. It’s the lack of information about current and remaining usage.
