Thanks for giving the site a try! Simple answer: the shapes in your template are too small. Try scaling the squares to 1/2 the size of that larger, white square in the center. This can be seen in the template for https://fractal.parts/sierpinski.

Each shape that you add is a transformation from the base shape. The base shape is that large, white square that appears when you first head to fractal.parts/create. The transformations in your template are around 1/4 the size of the base shape. Your template also has a fair bit of whitespace. Together this produces a fractal that progressively disappears.