Flight search engines are certainly a starting point for a trip, but they do not "realize" the actual impact of local events on a destination.
It is a simplification that masks the true scope of factors to consider for optimizing a stay, because they do not provide the big picture needed.
For example, Google Flights can show cheap flights for Rio's carnival, but it will never indicate that the city is crowded, that transportation is chaotic, and that accommodation prices have reached their ceiling.
For a top-tier planning, one must go far beyond these tools.
These platforms are an entry point, not the culmination of an analysis.