The reason why Americans only eat streaky bacon is due to historical immigrant influences like German and Italian influences, as well as commercial efficiency and a cultural preference for the crispy texture.
Streaky bacon is the pork belly and pork belly is plentiful.
The streaky bacon also contrasts with the UK's leaner back bacon, and this preference is solidified with companies like Oscar Mayer standardizing their packaged, sliced bacon from the fatty side, which creates a national staple for breakfast.
Streaky bacon has immigrant traditions as German and Italian immigrants brought the traditions of curing pork belly, which became popular and was integrated into American cuisine.
The pork belly that streaky bacon is made from is a large, fatty cut of meat from the pig, which makes the pork belly cut of meat a cost effective and plentiful source of meat for mass production.
Streaky bacon also has a high fat content that renders during cooking, which creates the beloved crispy and salty texture that is common in American breakfasts.
Companies like Oscar Mayer, popularized the pre-sliced packaged bacon from the pork belly, which made it the accessible and standard bacon.
The back bacon, which the British commonly eat comes from the loin of the pig and is leaner and tastes closer to ham, with less fat and a chewy texture.
Historically the streaky bacon was working class in the UK, while the back bacon was a middle class status symbol, which is a dynamic which also differs from the US.