Cannot aggregate by "chrom" field

[ravila4]

I tried running this query: https://myvariant.info/v1/query?species=human&facets=chrom

It fails with:

search_phase_execution_exception
"Fielddata is disabled on [chrom] in [superhot_hg19_20230505_hozqpqi5_202305251519]. Text fields are not optimised for operations that require per-document field data like aggregations and sorting, so these operations are disabled by default. Please use a keyword field instead. Alternatively, set fielddata=true on [chrom] in order to load field data by uninverting the inverted index. Note that this can use significant memory."

Is there any reason wy chrom is a text field instead of keyword?