Because consciousness is the indra’s net. Your projections are mirrored and reflected back to you from everywhere.
Like when you love an object, you will feel the object loves you back too.
When you love a person, you will feel that person’s loves you back too.
When you love the world, you will feel the world loves you back too.
When you hate the world, you will feel the world hates you too.
Even the masks get projected back to you many a times.
For example: If you project hostility with the mask of civility – you will feel others are doing the same thing. That they are hiding hostility behind their civility.
Another example: If you hate the world, but are just acting nice – you would see others the same way, that they too act nice, but inside are hating you and the world.
So your own mind is externalized and the projections you give out are mirrored back to you from other people, world, and its objects.