That's_ not the cause though, most if not all languages have been influenced by many others. And pronunciation, meaning of words etc drift over time in all of them as well.
Most countries have gone through the process of revising their orthography, changing spelling or even adopting different alphabets to have kind of consistent writing systems for their languages.
None of this has been done in the English language, it uses the most basic Latin alphabet which was made for a very different language (when even many Romance languages directly descending from Latin have adapted it with new letters or diacritics), for example English has a lot of vowel sounds that Latin hadn't and it even went through something called 'the great vowel shift' when changes in some vowel sounds got them closer to others that were 'pushed', these pushed others causing a sort of shuffling in the (finite) vowel space, but spelling didn't reflect most of this.
In fact I think that in some cases the spelling took the more ancient version that matched the pronunciation even less like 'plumb' (don't quote me on this, its from the top of my head)