I think we told you the explanation

That is because the rules to form the syllables are different. When there are two consonants between two vowels, the first consonant is joined to the first vowel; the second, to the second vowel. "E
studiar": es -tu-diar; pe
ntagrama: pen-ta-gra-ma. "Study" doesn't have an "e" before the "s", but por analogía (

), we follow the former rule and create an "e" before the "s",since the sounds "st", "sp", etc. don't exist in Spanish at the beginning of a word, but "est", "esp", etc. do.
Edit: ah, you meant historically. Esas cosas las dejo para los eruditos en la materia