Why isn't the query bound to prefixes with such config

[ch-sander]

Why isn't the query bound to prefixes with such config

<spar-natural 
            src="/static/sparnatural/config.ttl"           
            endpoint="https://g17dev.dhi-roma.it/sparql"
            lang="en"
            defaultLang="en"
            distinct="true"
            limit="10000"
            debug="true"
            prefixes="grace:http://www.graceful17.org/ontology/ g17:http://www.graceful17.org/resources/ "
        ></spar-natural>

The sparql will still be rendered like

PREFIX rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>
SELECT DISTINCT ?archive_1 ?archive_1_label ?GIS_2 ?GIS_2_label WHERE {
  ?archive_1 rdf:type <http://www.graceful17.org/ontology/archive>;
    <http://www.graceful17.org/ontology/called> ?archive_1_label;
    <http://www.graceful17.org/ontology/wkt> ?GIS_2.
}
LIMIT 10000

I must be missing something here...sorry!

Originally posted by @ch-sander in https://github.com/sparna-git/Sparnatural/issues/620#issuecomment-2399235368