This is mostly due to the difficulties scaling DistributedLog more so than BookKeeper. DistributedLog basically had no contributors other than Twitter and was just too big of a mountain to climb alone. The blog post you linked goes somewhat into this but that is ultimately why the choice to transition away was made.

Pulsar likely would have been considered if it was more mature at the time and sported a community of comparable size to Kafka (it's still a long way from this).