This is a good question.
The answer is simplicity and robustness. HBase is a very complex system. It's a monster to configure and operate. If you don't need random write capabilities and a K/V data model is sufficient for you, HBase may be overkill.
ElephantDB has very little moving parts, so it "just works." Additionally, if you make an update and write bad data to ElephantDB, you can easily delete the bad version and roll back to a version with good data.
At the end of the day, they target different use cases.
