Because the Tesla's they tested and have owner data for do not score over 75% on their scoring system. That does not account for numbers sold but tries to assess how good a car it is. See comments above.In defence of this video, while the delivery is a little blown out of proportion, I am interested to know why Which? didn't feel a Tesla qualified for the 'best electric cars to buy in 2021' list - given their huge popularity
For years I ran a series of ICE Ford Focuses. For much of the time it was top or second top bestselling car in the UK. It has never been a Which Best Buy. Largely due to its average level of reliability as I remember.