This is due to a combination of factors-- the choice of implementation language (C++), a variety of enhancements to RocksDB, consistent reads from leaders (using leader leases) rather than doing a 3-way quorum read, etc. We discuss these aspects in more detail here:

[1] https://blog.yugabyte.com/how-we-built-a-high-performance-do...

[2] https://blog.yugabyte.com/enhancing-rocksdb-for-speed-scale/

[3] https://blog.yugabyte.com/low-latency-reads-in-geo-distribut...