"Lazy" translations.

[Namill]

It's more of an general question rather than typo report. I'm just wondering why do translators often decide to translate things differently when there is no particular reason to do so, or simply omit some things in translations. For example in English version after receiving thanks from a rescued child Vidofnir says "You are welcome, child" while in Japanese one she says something along those lines : "Do not worry about it, a man's life is short and fragile, you should treat it with care". Something like that happens really often. I understand that sometimes a direct translation is not appropriate, but there's no reason not to do it when it's perfectly possible. Moreover, not translating some sentences is even a bigger mistery to me. Sometimes I feel like I listen to one, and then read a totally different dialogue.