why not use spark datasource in DeltaStreamer

[songj songj]

hi, I have some questions:

1. DeltaStreamer  has its own Source<JavaRDD<String>> to consume source
data,
such as Kafka, why not use spark datasource directly ?

2. Hudi has lots of logical which use RDD, why not use Spark DataFrame?

I just want to know the background of the above implementation, thanks!