I used to think it was just a social in-group/out-group thing, so English speakers could more easily spot foreigners for not knowing the odd pronunciations. But the more I learn about language the more I think of the adage "don't ascribe malice to what could be adequately explained by incompetence".

With how many speakers use English, I now think it just gets jumbled and mangled over time and there's no real central authority to correct for that. Ultimately that makes our words sound weirder and more colorful so it's not the worst thing, especially once you understand that even native speakers don't know how to pronounce most large words until heard.