““The value of Prime to customers has never been greater,” said Olsavsky. But, he says, it’s also expensive. “The cost is also high, as we pointed out especially with shipping options and digital benefits, we continue to see rises in costs.””

— https://www.engadget.com/2018/04/26/amazon-raises-prime-fee-to-119-in-the-us/

Don't be fooled. The increase in cost of Prime is a calculated move by Amazon on the stickiness of the program. Amazon continues to use the cash flow from their Prime membership base and AWS growth to invest in their international expansion and offset the cost of logistics. This is one lever they know will likely see very little churn with a 20% increase. Bezos' #1 job these days is about effective capital allocation and this a well played move.