View this as an insurance and it suddenly all makes perfect sense. You pay a little more so if this month your usage pikes, you won't get a surprise invoice you didn't budget for, and you won't get cut either. At worst, you'll get rate-limited. This price stability is valuable and paying extra to get it isn't being charged an unfair price. Of course if you don't find it beneficial, you should choose another offering.
This is only relevant because the cost of bandwidth is excessively high--much higher than it should be--and so people essentially need to pay for this gouging-insurance.
