For Cake the major benefit is not to have to manage streaming infrastructure. When event data exceeds the kinesis shard limits, scaling out happens easily without having to make any code changes. Extra shards are added and an extra backend worker can start processing the extra shard.
Data security is handled by AWS KMS, allowing to transparently encrypt & decrypt streaming data. AWS Kinesis also nicely integrates with the existing Identity & Access Management infrastructure (IAM) that AWS provides, ensuring authentication and authorization controls.
Finally, one sometimes overlooked benefit is that Amazon Kinesis integrates with other AWS products. For example, Kinesis can easily store all the data passed through its stream in S3, by also sending the data to Amazon Kinesis Data Firehose.