A lot of these answers are working towards the idea of having consistent grapheme (letter or letter combo) to sound (phoneme) relationships. ie the letter 'a' would always represent the same sound, and that sound would always be represented by the letter 'a'. This is called ideal phonemic orthography.
English has whatever the opposite of phonemic orthography is; depending on your accent, the letter 'a' has about 7 sounds the most common being 'o' as in 'what'. It's extremely unhelpful when teaching kids to read English.
Languages seem to pick up a lot of cruft over time as they grow, absorb loanwords and just change because language, so you usually only move towards phonemic orthography with some deliberate act, usually by the government.
An example might be Indonesia really wanting a national language to tie a very diverse population together after the second world war. I think they still have a government department who makes pronouncements about the language. The result of this is you could learn to correctly pronounce Indonesian in about 10 minutes, and read an Indonesian newspaper to a native speaker and it would be almost entirely intelligible to them even though you didn't know the meaning of what you were reading.