To a first approximation nobody plumbs toilets into the storm sewers for practical reasons.
# Solid human waste will clog the smaller pipework and now your toilet waste is overflowing inside the home and the occupants are very angry
# The fittings don't "fit". The local plumbing supply store has the adaptor you need to run grey waste into rain water drains, even if it says that's not what it's for, but it does not have adaptors to run a large diameter soil pipe into the storm drain, that's a recipe for disaster they want no part in and the part has no other purpose.
If you indicate that you've got some "good" reason to attempt this, they'll sell you an expensive macerator which solves the first problem by grinding up waste, and as a result the output is smaller diameter waste pipes - but now your project is more expensive and more complicated to install.
# Solid human waste will clog the smaller pipework and now your toilet waste is overflowing inside the home and the occupants are very angry
# The fittings don't "fit". The local plumbing supply store has the adaptor you need to run grey waste into rain water drains, even if it says that's not what it's for, but it does not have adaptors to run a large diameter soil pipe into the storm drain, that's a recipe for disaster they want no part in and the part has no other purpose.
If you indicate that you've got some "good" reason to attempt this, they'll sell you an expensive macerator which solves the first problem by grinding up waste, and as a result the output is smaller diameter waste pipes - but now your project is more expensive and more complicated to install.