Early HTTP even provided bits and pieces of a mechanism to pay for content, and browser extensions with integrated with crypto wallets have shown that it's feasible to do reasonable secure transactions within those browsers.
So, why can't I pay a dollar or two to read an interesting article, or pay something to the author of a cool github repo? Or on the other side, why can't I as an author just place <payme iban="xxx" placeholder="1 USD">Buy me a banana</payme> and be done with it?
Did the role get taken over by easy-to-use payment gateways like Stripe? Do card processors still take a fee too large for the idea to be viable?
Just any sort of refund or chargeback process might wipe out hundreds if not thousands of transactions value. Too little value to be sensible.