That's because we literally don't know much. EG.5 has only had 183 sequences submitted to GISAID, and EG.5.1 has had 3400 sequences submitted. This means we only have about 3600 cases confirmed as EG.5, but it's growth rate since May is crazy fast. 10% of sequences submitted to GISAID by the end of July were for EG.5, compared to 0.02% in May.

Part of the problem is that people have stopped going to the doctor when they can just do a COVID test at home, so we are less able to track individual strains and calculate things like transmission rates. When's the last time you heard the phrase "contact tracing"?

Source: https://GISAID.org/lineage-comparison and also I work in COVID monitoring.