People live in new, well insulated houses. Or small houses/flats, or are out a lot.
They're on fixes from 6-12 months ago, when prices were much lower. The average bill at that time was around £100 pm.
They pay monthly/quarterly, are talking about summer use and aren't accounting for higher autumn winter use that's coming that will cost more per unit too.
They don't have their heating on much, never at night, for example.
They don't wash towels and clothes after one use/wear or use the quick (but counterintuitively more expensive) washes for all their washing, which they then line dry instead of tumble drying.
They don't take multiple long showers daily or more often. They might, shock horror, shower less often, or shower at the gym/work.