> I think the fraction of people who have a clear enough mental idea of the dimensions or volume of an Olympic-sized swimming pool is pretty small relative to the articles readership

At least in the US, "Olympic sized swimming pool" is as common a unit of measure as a US football field - very commonly used.

I agree. It is common to see those used as area and volume examples. I think it is far less common for the audience to have a clear mental picture of the two terms though. It's easier for a football field to serve as a reference because more people have exposure to football fields. It is more difficult for an Olympic sized swimming pool to serve as a reference because there are fewer people who have seen one in person.

I think it is a bit comical to use swimming pools as a volumetric reference when most people's experience with swimming pools has been in a back yard setting or on visits to community pools, which may be any convenient size.