Can you name a provider? I personally use Stripe Tax for my business and while they will calculate the taxes you owe in each municipality it is totally on you to create an account with each country/state's Department of Revenue and fill out a form quarterly to submit your payments.
This paperwork is what I believe a marketplace like the App Store or Amazon do for you under their own entity that you have to do yourself if you bypass their stores.
You could consider using Galvix, which will connect with your billing system (including Stripe), fetch all the invoices and automatically prepare and file sales tax returns across each of the US states where you are legally required to file, all while providing you full control and visibility over the process. Galvix charges a flat fee of $75 per filed return, which can be considerably more affordable compared to paying a revenue share to other platforms (if tax compliance is the only reason you want to use these platforms).
What's wrong with your Amazon example? They don't charge as much (and that's partially because, while they're big and dominant, they're still not as big/dominant in that market)
This paperwork is what I believe a marketplace like the App Store or Amazon do for you under their own entity that you have to do yourself if you bypass their stores.
Please correct me if I'm wrong.