Because it's perfect, that's why. ok I don't ship Johnlock but this is epic. <-- I'm not gonna take this as Johnlock but instead as uncle John reading to Sherlocks and Molly's son Hamish<<how can you not ship Johnlock? This is Johnlock!
In "A Scandal in Belgravia" Sherlock calls Lestrade to tell him that there's been a break-in at Baker Street. Sherlock tossed the American out the window, repeatedly. Lestrade would have had to explain it without implicating Sherlock in a crime.
The classic Holmes, ‘Okay, yeah I did something kind of appalling but I love you very much in my own messed up way, please don’t be mad’ face. I love the way both of these interpretations of Sherlock are so different, but so well done.