Small Iceberg file sizes

[shanebusenitz]

We have a Trino cluster running on 2 nodes using the Iceberg connector and tables created using DBT. Most tables are partition by a run date or buckets. In all my tables the file size is really small (hundreds of files under 1 MB). Even if I try running something like:
ALTER TABLE iceberg.dev.my_table EXECUTE optimize(file_size_threshold => '256MB'); I still end up with KB files and end up with more files.

What am I missing that will actually condense files into larger sizes?