Follow the incentive: the idea that a travel guide could reduce thermal comfort to a simple humidity-temperature equation, even if it seems useful, roughly simplifies reality.
It's the kind of convenient generalization that facilitates the sale of a book but ignores concrete and essential factors.
For example, in Dubai, it is oppressively humid and hot, but comfort is ensured everywhere by air conditioning, making the travel experience very different from just reading data.
The motivations behind this simplification are clear: to offer easy-to-digest advice, even if it lacks practical nuances.