Most encoders let you define filters that restructure the data using out of band knowledge to achieve better rates. For example, if you have an array of floating point numbers, rearranging the exponent and mantissa can yield significant savings if you can arrange for a consecutive run of each separately because the generic compressor doesn’t know anything about the structure of the data. Compressors are great but out of band structural compression/reorganization + compressor will always outperform compressor alone.