Going from spelling to pronunciation in French follows (admittedly complex) rules that are rarely broken except for common words (or endings such as -ent). Vowel pronunciations for a given spelling are far more variable in English, and often depend on the etymology of the word. Plus, English has word-level stress that is not marked in writing (French has none, and it's marked in Spanish), and moving the stress will usually make a word unintelligible! That alone makes writing => pronunciation very difficult.