Alissa G. answered 06/28/19
English & Spanish Language Lover-Grammar Geek-Word Nerd
Lots of reasons! While basic English grammar is simple in comparison to other languages, English also has many, many more words and colloquialisms. The fact that English is spoken as a native language in different countries across continents (U.S., Canada, Belize, England, Scotland, Ireland, Wales, Australia, New Zealand...) tells you right away that a wide variety of cultures have all different influences on the language. Additionally, modern English takes root in many other languages and some of our words are clearly from these, such as German, Greek, and Latin, while others are borrowed from modern languages like French ("bouquet") and Spanish ("rodeo", "armadillo", "tortilla"). Therefore, the spellings of English words often do not follow a pattern, and neither are they phonetic (the words are spelled sometimes vastly differently than they are spoken).
I have experience learning and teaching Spanish as well as teaching ESL, and I can tell you that Spanish is a prime example of a phonetic language whose word spellings stay true to their pronunciation (according to the Spanish alphabet). In other words, you will always know how to spell a word in Spanish if you hear it spoken, even if you have never heard of the word before. Likewise, you will always be able to pronounce a word in Spanish correctly from reading it on a page, even if you have never seen the word before. This is most definitely not the case in English!
I hope that helps.