If you ask someone if something can or can’t be considered ‘mainstream’, the usual response involves numbers. User numbers, audience numbers, profits. Stuff like that.
The thing is that the idea that large audiences = mainstream is essentially fallacious. You tend to get much larger audiences for mainstream things, but not always. Something that is mainstream can have very small numbers indeed. Then we say it has ‘niche appeal’. Quite a lot of things we think of as mainstream fall into that category.
