Why are my new figurines have high levels even if I haven't invested in them yet?

This is likely due to the Otaku Committee effect.

This is a very useful feature of Otaku Zone where you can place the top 5 figurines with the highest levels to serve as committee managers. The additional figurines you’ll place will have an instant level boost up to a certain level depending on their quality.

This will allow you to use new, low-level figurines in your current teams without spending upgrade materials. Since this level boost is only applicable as long as the figurine is displayed, you’ll need to remove the figurine from Otaku Zone in order to upgrade it using the standard upgrade materials.