Why is a dehumidifier either a hack or a lie?

smartvacuums.co.uk says a dehumidifier collects 10 - 20 litres of water a day. dehumidifier-rentals.co.uk says 8 - 20 litres a day for a domestic compressor type, or 0.5 - 10 litres per day for a small domestic type. upgradedhome.com says about 4 litres a day.

Sounds plausible for a mop water bucket to fill usefully full between, say, twice-weekly moppings.