Of the services on offer, only payment processing has significant cost to Microsoft. Things like crash reporting are solved problems whose cost should be approximately equal to the cost of hosting the data.
Fraud reduction accounts for the majority of that percentage.
Patreon has established that they will completely go out of business at 5%.
Steam is taking 30% and Epic is taking 12%. Salaries, servers and regulation are expensive.
Microsoft offering 5% is a steal.
This is neither unique to PayPal or the actual floor.
2.9% + (roughly) $0.30 is pretty much the standard across all public facing credit card processors like PayPal (and their subsidiary Braintree), Stripe, Amazon Pay, Authorize.net, and more. I have heard rumors Stripe offers rates as low as 1.8% for large volume processors. Adyen charges $0.12 + 0.6% + interchange fee making them extremely lucrative for their customers (including Uber, Netflix, Etsy, Spotify).
Given Microsoft's size and expertise, I'd anticipate they are operating close to interchange rates around $0.10 + between 0.8% and 1.6%.