And many customers simply are not doing petabytes per month.
AWS wasn't meant to support Netflix type loads, those guys will build their own CDN's. For everyone else who wants security groups (totally for free) when some other firewall vendors would charge a small fortune to provision 1Gbps capacity for these types of services... they are fine with the price.
The other issue cloudflare doesn't understand is the bandwidth pricing they quote is for capacity (ie, 10Gbps). AWS has to have enough capacity to serve the peak, but the customer only has to pay for data used. I'm sure at low points the data is free, but maintaining the black friday / superbowl capacity is expensive, so you are paying a premium for that too.