Because some places, like Europe, use the comma symbol as the decimal point, so pi would be 3,14159...

That doesn't make sense. Everybody knows that the number of views a post has is an integer, it doesn't really cause that much of a confusion for anyone. Most europeans are used to it.

What they should do is display the right separating symbol depending on the user's location.

I wonder the same thing about youtube views count

I do see commas on YouTube's views count.

I sometimes see commas on YouTube's views count, seriously. I think it depends on your location.