Primary reason at the moment is that elasticsearch currently has no backup/long term durability story. They plan on something for 1.0, but that doesn't help with the current situation.
Also we've suffered data loss on several occasions with elasticsearch. This has been getting better but is still a concern. Having the external long term datastore and a handy import method made these small hiccups.
Lastly IMO elasticsearch works best, particularly when working with log like data, as a rolling window view into the data. This keeps your elasticsearch cluster to a reasonable size (saving $$) while keeping the ability to re-load old data for exploration when you need it.
Also we've suffered data loss on several occasions with elasticsearch. This has been getting better but is still a concern. Having the external long term datastore and a handy import method made these small hiccups.
Lastly IMO elasticsearch works best, particularly when working with log like data, as a rolling window view into the data. This keeps your elasticsearch cluster to a reasonable size (saving $$) while keeping the ability to re-load old data for exploration when you need it.