Archives have different types of information on their website. The genealogical indexes are often found in a different section than the finding aids with the archival descriptions or catalogs. These descripts are often quite generic and describe whole series, like minutes of court records, incoming correspondence, or tax records. If you are lucky, the archival descriptions in the finding aids will also include names of people. Some archivists have made the effort to add the names of parties to finding aids of court records, for example, or to include abstracts of medieval charters.
If you are doing research, do not just search the indexes, but also make sure to search the finding aids.
Example: Dirck van Grevenbroeck
One of my ancestors is Dirck van Grevenbroeck, a brewer from Loon op Zand in the late 1500s and early 1600s. A search for “Grevenbroeck” in the finding aids of the Regionaal Archief Tilburg turned up a charter from 1587 whereby he received a rent of 24 guilders.