Here's why:
* Latin was the dominant language of learning: Gutenberg's printing press was revolutionary, but it was primarily used to reproduce religious and scholarly texts, all of which were written in Latin.
* English was not widely used in print: English was primarily a spoken language at the time, and its use in printed materials was limited. Early printed English texts were mostly religious or legal documents.
* Gutenberg was German: While Gutenberg was a significant figure in the history of printing, he was German, not English. His primary interest was in printing materials relevant to his own culture and language.
It wasn't until later, with the rise of the English vernacular and the development of a printing industry in England, that the English language became more prominent in print.