Italians fill single baskets with 7 grams, doubles with 14, and do not use triples. Double baskets are used to make two singles. People in Italy overwhelmingly drink straight single espresso, ordered as "un cafe." Cafes rarely make milk drinks, since most people have them at home, in the morning. This is the custom in the rest of the Mediterranean as well, where Italian prep norms hold.
Properly made, an Italian espresso has a soft, smooth taste due to the high extraction.
Espresso became fashionable in Northern Europe and the US in the late 1950s, when it was drunk Italian style; but in the 1980s, coffee shops used espresso machines to make milk drinks or cafe crema. In these, coarser grinds and higher doses work better, especially as roasts got darker. The Italian style of soft, highly extracted coffee gets lost in milk or very long shots; while the sharper tastes in higher doses of less extracted coffee are perceptible.
Since the mid 2000s, the emphasis at the high end has returned to straight espresso. Also roasts have gotten lighter. Therefore, finer grinding has become mandatory in order to get highly extracted shots in the soft Italian style. The simplest solution would be to return to the lower doses used in Italy. However this has not happened. Instead people are going through hi tech contortions to get ultra fine grind shots in huge doses. One way to do this is special baskets with larger holes. But this has limits. Another way is to go to Turkish grinders that produce fewer fines. It is the fines that control the flow through the puck; so with fewer fines, you can have a larger doses of very fine ground coffee that don't jam the machine.
(Caveat: I went back to Italianate 14 gram doses. Since then I've stopped being an espresso authority, since I no longer understand the mysteries of extraction and grinding. So take this explanation with a grain of salt -- its physics is correct, but it does not comprehend the mysterious paraphysics of modern espresso.)