In broad strokes, the reason is because the line has to be drawn somewhere. If you want, you can read https://en.wikipedia.org/wiki/Wikipedia:Existence_%E2%89%

In broad strokes, the reason is because the line has to be drawn somewhere. If you want, you can read https://en.wikipedia.org/wiki/Wikipedia:Existence_%E2%89%A0_Notability https://en.wikipedia.org/wiki/Wikipedia:Existence_%E2%89%A0_... and the links there to gain some idea of the reasoning behind it.