When creating a new BigQuery export you can choose to create tables partitioned by the
date column. Partitioning tables is recommended, as it increases performance as well as reducing the costs of your BigQuery queries. Partitioning is on by default for new exports.
You can read more about why you should use partitioned tables here: https://cloud.google.com/bigquery/docs/partitioned-tables.
If you don't want partitioned tables you can disable it when creating a new export under Advanced settings.
Why can't I change partitioning on existing exports?
BigQuery does not allow you to change partitioning on an existing table, instead you have to delete the existing tables and create new ones. Funnel does not delete tables, as this would risk losing important data or breaking steps in your pipeline.
If you do need to change the partitioning in your export you can delete the BigQuery dataset yourself and set up a new export. Don't forget to disable or delete the existing export!