With the latest booking system wardens will know if any Motorhomes are booked in, and if insured with the caravan Club the exact make and model, as this shows up automatically on the booking confirmation.
Motorhomes can cause problems on grass, especially wet grass, by sinking in. So with this knowledge, to protect the grass for future use by members, they will allocate hardstandings to motorhomes.
Once in the past, although i prefer hard standings, i had to go on grass for this very reason but at least the grass pitch was in good condition.
Hamer