Why do they call all Americans "English" ?

Beginning in the High Middle Ages all Germanic languages east and north of the "Welschen" (Romance speaking peoples like French and Italians) and south of Denmark were then called "Deutsch, Dütsch, Dutsch, Deitsch, Duits, Diets". The speakers named themselves after that but retained strong tribal (Saxon, Frank, Swabian, Bavarian etc.) and regional identities (principalities or towns like the Palatine or Cologne). You may have heard about the "Holy Roman Empire" that was essentially the East Frankish Kingdom (9th century) morphed into the Regnum Theutonicum (German Kingdom) or Regnum Theodiscorum (Kingdom of the Germans) plus some Romance speaking countries after the Frankish Carolingian royal dynasty was followed by the Saxon Liudolfingers (Ottonians) at the beginning of the 10th century. Theutonicum or Theodiscum being the latinization of deutsch,.... meaning "like the people" creating a medieval ethnic identity in distinction from Romanic neighbours to the west and south (Welsche, comp. "Welsh") and Slavic neighbours to the east (Wenden). Therefore the English named the people from the mouth of the Rhine to the source "Dutch". The English noted differences based on the "High German Consonant Shift" (or Second Germanic Consonant Shift) (e.g., machen vs maken, Dorf vs Dorp) when travelling from north to south along the Rhine. They called the Nederlandish/Low German languages "Low Dutch" and the High German languages "High Dutch" because "Low Dutch" in the north was spoken along the lower courses of rivers like the Rhine and "High Dutch" in the south was spoken along the upper courses of the rivers flowing north. For translating the bible Luther used a chancellery language derived from East Central New High German. Standard German (Hochdeutsch) rapidly expanded for writing except in the Low Countries but the common people spoke their regional dialects until the 1950's (even longer in the south) learning Standard German in school for writing and communication with speakers of other dialects. Since the 17th century the English used "Dutch" only for Nederlands. Since then they used "German" for Hochdeutsch (Standard German). But the Americans used "Dutch" longer also for Germans and whatever they spoke. Pennsylvania Dutch (or Pennsylvania Deitsch) belongs to (West Central) High German because it has most of the changes that represent the High German Consonant Shift. It's strongly related to the Palatine dialects. Please do not confuse High German (in the sense that it conforms mostly to the Consonant Shift) with Standard German (High German/ Hochdeutsch). It's called Hochdeutsch (High German) because it was first established as the language of literature but wasn't the spoken language of the common German until the 1960's. Standard German was derived from East Central High German that sounds very different from West Central High German dialects. Therefore Pennsylvania Dutch sounds different from Standard German (Hochdeutsch) but both are mutually intelligible.