Why is Belarus called "White Russia"? In Chinese Belarus is 白俄罗斯, which literally means White Russia. But I don't understand why it is called as such.

If you get more rigorous with the pronunciation, it is more like be, but since there seems to be no word to be pronunced be in Chinese, maybe bei might be preferrable. So 呗俄罗斯 or something like that.

Also why is it not more direct, such as 被拉入式 or something like that?

Is this related to some historical or political reasons? (Especially because 黑 is considered a bad word)
Because the name is also translated according to its original meaning.


  白俄罗斯在本土语言中是Беларусь，其中前面的Бела是“白“的意思，剩下的是“罗斯”的意思。


白 comes from the front part of the original phrase Беларусь, i.e. Бела, which means white.

and


  白俄罗斯人是东斯拉夫人的一支，根本不属于俄罗斯民族。白俄罗斯人称自己为“别拉罗斯”（音）人，如果完全按照音译国名就是“别拉罗斯”。“别拉罗斯”的俄语翻译是
  Беларусь 由“Бела”（白色）和русь（罗斯）两部分组成。应该翻译为“白罗斯”。
  
  英语可能是从俄语再译，是 belarussia 。可能是因为当时的翻译者，从英文的russia联想到俄罗斯，又因为俄文中的 Бела
  （白色），再加上对白俄罗斯人的历史没有常识，就想当然地翻译为“白俄罗斯”了。


references:
【风俗文化】其实，每一个“斯坦”国都有自己名字的由来
国名的疑问为什么叫白俄罗斯?因为他的人比俄罗斯还白?
俄罗斯、白俄罗斯、乌克兰等名称的由来及其它