data lego for high performance computing
most blockchains use LSM trees and tout their write optimization. Hashmaps are much much more read optimized than lsms. from wikipedia As increasingly more read and write workloads co-exist under an LSM-tree storage structure, read data accesses can experience high latency and low throughput due to frequent invalidations of cached data in buffer caches by LSM-tree compaction operations.
on hashmaps read optimizations:
In many situations, hash tables turn out to be on average more efficient than search trees or any other table lookup structure. For this reason, they are widely used in many kinds of computer software, particularly for associative arrays, database indexing, caches, and sets.