If you look at London Heathrow in terrain mode on Google Maps no planes are visible. Most other airports have at least some planes visible at the gates. Why is this?
in Google Earth it says it was taken 10/04/2020<p>1. That was during the first corona lockdown. In that case, the airport would mostly be closed. However news reports say that the airports were kind of open with some flights flying during lockdown (massively reduced - 60 vs 600)<p>2. Looking at the date gives another clue. April 10 is Good Friday, the Friday before Easter weekend. Good Friday is a big national "bank holiday" when most things are shut in the UK. Therefore even less flights that day.
I assume you mean satellite and not terrain mode. Terrain mode doesn't have images so there are no planes visible at any airports. As for satellite mode I looked briefly and noticed 2 planes.
I see the same suspicious lack of aircraft on the ground. It's really interesting. I see one Qantas aircraft taxiing onto runway 09R, and a Saudi aircraft taxiing into parking from 09R, and that's it. Also interesting is that I see a bunch of trucks on both ends of runway 09L. The Google Maps imagery of other major airports, and even military airfields, shows <i>many</i> aircraft on the ground.
Very few parked cars too. I see the same phenomenon at London Gatwick Airport as well. Perhaps an internet sleuth can find out what time the image was captured (e.g. the control tower has a distinct shadow that can be measured) and see if it lines up with any specific event.