It's pretty much like not giving you the car speedomoter, and then the city places speed trap cameras all over the city and then after a month, you get a bill for $200 because you went over 4 times.
This business make money first mentality is pretty bonkers.
The internet provider offers a service with certain penalties that are typically made clear enough if you read the contract. It is up to you, through whatever means you have available, to not use it in a way that gets you excess charges.
I like your speed trap analogy but I still don't think it is the ISP at fault. If you can't afford the overage and your phone has no metering then there are plans and pre paid plans available to suit that need. You are still the one signing up to the service and using it, you don't have to if you think the situation is unfair.
None the less, it is definitely a balance of transparency and I think it is fair to ask for app vendors to properly optimoze and advertise the data usage of their apps in some way.
People can understand it, but they usually don't habitually check it, resulting in surprise bills.
Some angry support tickets might be warranted though!
If I go to the gym and drop 100kg on myself then it is my fault for not understanding the risks, where it is reasonable to do so.
It is reasonable to expect you as a customer of the internet service to understand the service you are using and the costs involved. It really falls on no one elses shoulders.
I do agree that it tends to be over priced and the pricing structure is often confusing but I still think it's within the grasp of most to understand it.