Arguably there are benefits to developing in-house expertise, and no better way to develop expertise than to architect and build a solution end-to-end. Twitter now has several domain experts on staff who can continue maintaining DistributedLog and/or weigh its benefits against Kafka's and make more informed decisions going forward.

Not saying that they couldn't have worked more closely with Kafka's team in the first place, but, hey, now we have two Kafkaesque log services instead of just one. Seems like a win to me.