“S3 is the only object store that doesn’t support preconditions.”
GCS and Azure Blob Store both offer compare-and-swap. S3 doesn’t, so anyone building on it bolts on DynamoDB to get safe writes, which is another AWS bill. The low-latency answer, Express One Zone, runs $0.16 a gig, twice the price of gp3 EBS, and lives in one zone. AWS has no reason to fix a gap that sells a second product.