Dynamodb experienced a severe outage in us-east in September of 2015, dropping the service to three nines of uptime on just the single event. During the incident there was little-to-no knowledge of when service would be restored, so companies that relied on the service were flying blind.

Such an outage can sometimes be mitigated when operations are internal to a company; but with DynamoDB, one has to build internal failover or implement a complex cross-region replication scheme. The complexity and reliability starts to reduce the attractiveness of the hosted service in general.