The Power BI service partitions data based on date range. This is what enables only certain partitions to be refreshed incrementally. To make this work, the partition filter conditions are pushed down to the source system by including them in the queries. Using Power Query terminology, this is called "query folding". It is not recommended that incremental refresh is used when the required query folding cannot take place.
Reference:
https://powerbi.microsoft.com/en-us/blog/incremental-refresh-query-folding/