GCP and Confluent partner to deliver a managed Apache Kafka service

Why would someone want to use Kafka rather than PubSub? For a nonexpert, it seems like PubSub is just a tighter abstraction---same basic operations, fewer knobs to turn. Are there important features in Kafka, that aren't in PubSub and can't be easily built on top of PubSub?

I love Kafka and the log orientated streaming model, but I often have to think twice before recommending it to clients who would have to manage the ops themselves. Having a managed service on GCP, and Confluent's existing cloud offering on AWS really brings down the barrier to entry. There aren't really any AWS/GCP serverless equivalents (Kinesis has 7 day retention maximum, no key compaction, and less surrounding tooling such as KStreams/KSQL).