The internet is a place for people from every country everywhere. When you create a site/forum on the internet, you should consider what kinds of people will access it, from what regions they come.
If your site is supposed to cater for people from all over the globe, then you will want to use the most popular/widely used language available, which at the moment is English. With all its rules and everything.
If people want to develop a language of the internet, they are free to do so, but they must either somehow make it official or convince people to use it, detailing its advantages over other actual historical languages.
Long story short, this site uses English as its official language (don't try to deny that). As such, just as when you try to visit an English-speaking country, the better you know the language, the easier it is to communicate.
And communication is one of the central aspects of the internet.