Introducing The Universal Religion

[Sword of Christ]

Oh but there is ample of evidence for materialism

There's evidence for material things but that could have all been created by God or is underpinned by an eternal non-material conscious or purpose driven force. Materialism who state that only the matter exists, the matter in itself has no purpose or intelligence but can somehow create intelligence when it is arranged in a certain form such as the human brain. You can't prove either scenario just by looking at the material stuff we can see though therefore it's a case of what you believe to be true.

Theism makes some strong positive existence statements of very complicated and unseen things

Materialism is the statement that physical matter/energy is eternal and is all there is exist and our existence is dependent upon matter arranged in a form. It's not something you could see and demonstrate to be true it's just what you believe is true. In sense you're really only doing the same thing. This is an idea/philosophy about the ultimate nature of existence.

and the burden of proof is on you.

You can't "prove God" and you can't prove your materialist philosophy either so it's a stalemate.

You can't just make up anything you want and then claim that just because it unfalsifiable

You're doing the same thing yourself even if you don't understand that you're doing it. You can't really claim atheism/materialism as the default either seeing as belief in the unseen aspect of reality seems to be as old as the human species itself.