Historically, we have always checked conditions before planning a trip, long before the "rainy season" was the only determining factor.
The old manual teaches us that weather influence is a condition, not a main cause.
School holidays or local events have long had a much greater impact on prices and decisions.
Take Christmas holidays for the Canary Islands, where prices soar much more than because of rain, even if the weather is less ideal.
Budget prudence and common sense prevail over a simple downpour.