1. We changed the source code too much that we are not able to merge it back to RocksDB easily (This project started at 2016 as an close-source project) 2. We have different road path with RocksDB (e.g. We will remove a lot of un-used code to make TerarkDB much more light-weight than current version in the future) 3. We have lots of third-party partners (e.g. Intel, on Opatane SSD/Memory and others with ZNS...) may participant in this project so we want to handle all commits ourself to make sure everything is under control.