During the High Middle Ages, why wasn't Germany able to develop strong centralized monarchies but England and France were?
The primary reason Germany was not able to achieve a strong monarchical government was because of ongoing disputes between the Popes and the Holy Roman Emperors which kept the Empire weak.
Germany was comprised of a large number of independent principalities under the umbrella leadership of the Holy Roman Emperor. Ever since Charlemagne was crowned "Emperor of the Romans" by Pope Leo III and Otto the Great was crowned "Holy Roman Emperor by Pope John XII, a conflict over where the division of authority between church and state was drawn. A number of Emperors, including Frederick Barbarossa and Henry IV were in constant conflict with the Popes over the extent the Emperors exercised over church property and appointments. Many Emperors claimed the right to appoint church officials within the Empire while others claimed the right to tax church property. The Popes often insisted that by reason of the actions of their predecessors mentioned above, the Emperors were at least nominally answerable to the Pope. Popes often incited princes and other rulers within the Empire to support the Church and actually wage war against the Emperor. This series of conflicts between Church and state kept the Empire loosely connected and prevented the Emperors from gaining sufficient power to united under a strong ruler.