Of course the best would be to let users pay for not seeing ads and then shove them in their face anyway for maximum profit.
By very definition 99% of ads that could be in the slot are not there because someone is not willing to pay that much to show that ad, except for the single one that won the auction.
Ads have a maximum cost at which they don't become viable/profitable anymore.
The only difference is that now the user could bid on that ad slot himself, to keep it empty.
If you look at the average ad revenue, that wouldn't be all that much money. Certainly a fraction of what it costs to become a no-ad subscriber currently in various platforms.
ApplePay is about as frictionless as digital payments can possibly be, and I still occasionally abandon a purchase because of some annoying authentication issue.
Friction. The vast majority of people are not going to go through the effort of setting up a digital wallet to browse, when the existing system allows them to do it for free.
Some people would for sure, but then you also need websites and creators to agree to participate in the scheme (or don't, and just unethically redirect ad revenue to yourself, like Brave used to).