Metrics systems hold their label-set indexes in memory, so cardinality directly multiplies in-memory index entries and causes memory exhaustion. Log and columnar storage systems write raw records and rely on dictionary encoding and run-length encoding to compress high-cardinality string fields efficiently, so a field with millions of unique values does not carry the same memory penalty. That architectural difference is why high-cardinality identifiers belong in logs or traces rather than metric label sets.