Amazon was using MongoDB without paying for it. MongoDB found that objectionable, and changed the license such that Amazon would either have to pay, or stop using it. Amazon stopped using it, and started using its own in-house implementation instead (presumably because it was cheaper to develop it than to pay MongoDB). So, MongoDB got exactly what they asked for. It's just that, when they forced Amazon to make a choi…
Which AWS service are you referring to exactly? AWS's existing json document DB is called DynamoDB and has nothing to do with Mongo.