Indeed. Many of the optimizations ripgrep (and the underlying regex engine) does only show benefits if the data you're searching is already in memory.[1] The same is true of GNU grep. This is because searching data that's in your OS's file cache is an exceptionally common case.

[1] - I'm assuming commodity SSD in the range of a few hundred MB/s read speed. This will likely become less true as the prevalence of faster SSDs increases (low single digit GB/s).