You can always just use the Fun and Politics streams - the other streams are totally optional, just another way to browse if you happen to enjoy it.
Allowing independent streams lets people experiment with their own communities with different rules, and sometimes with content that just wouldn't ever do well enough in the Fun stream. For example, Metal_Memes has really highly upvoted content as a separate stream because it's mainly people who care about metal music who are viewing the stream, whereas most of those memes wouldn't do well in the Fun stream.