Why is Bundler creating so many draft orders in my shop?
This is just how Bundler works. It applies bundle discounts by creating a draft order with discounted items and redirecting the customer to it.
If your bundles are popular, then Bundler will create a new draft order every time it applies the bundle discount. There is nothing to worry about. When the draft order gets paid, it will be moved to your shop orders. If you want, you can remove the draft orders which don't get paid in a timely manner.

If you don't want the app to apply discounts with draft orders, then you can turn on the feature in Bundler -> Settings -> Discount modes to apply the discounts with discount codes (instead of draft orders). However, it is recommended to apply the discounts with draft orders.