As the Devs said over here : After doing some digging, this is what's the cause of this issue: Back
in the early days of Roll20, Google's search engine API was free and
readily available to be used. This was utilized for our web search for
the Art Library. At the time, Google had claimed that this would be a
freely available asset for a long time. As you can probably guess where this story is going, they decided later to lock their API behind a very significant price tag. Nowadays,
when someone runs searches in the art library, it's using search
results that we scraped back when we still had the API available. Those
search results are tied to the keywords that were searched with at the
time. This list of compiled searches are nearly four years old now, and
limited to the keywords that were utilized by a fraction of the userbase
that we have now. Ideally, we would find another search engine
API to utilize, but so far we haven't found one that is financially
feasible to license. When things change it will be announced, but for now we're stuck with what we have.