To maintain consistency? I think there is value trying to keep a language somewhat internally consistent. I'm guessing that it makes the language easier to learn, at least in the future - less loanwords (or bastardized loanwords) might for example mean less grammatical exceptions.
Of course, it's not like one has to come up with a completely unique word for something, to make it not-like English. But one might want to adapt it to the language by for example translating the words that went into it (like "mouse" as in "computer mouse").
> This is a two-way street. Much of the english vocabulary comes from other languages:
English is also kind of a nightmare when it comes to phonetics, which last I read was due to all the different major languages that has been influenced by. But I guess it wouldn't be a problem if the spelling of the language was more consistent, and originally foreign words can be Anglicised to fit in, so I guess that isn't a problem because of old loanwords, really.