I love this analogy[0], but to play devil's advocate I do a lot of tipping in cash and it's kind of a pain to break down big bills, so I can see some benefits to normalizing more digital options that actually work.
My bank is digital, it doesn't have a local branch, and most ATMs around me dispense cash in $20 bills. So I can make a small purchase near the ATM if it's in a shop and then ask them to give me change in smaller bills, but usually there's nothing I want. I don't have a local branch to drive to, but maybe other banks would help split bills? It's not awful, but it is pretty inconvenient.
Of course, the way to fix that might not be for everyone to standardize on iPhones, it might be to just have more ATMs that dispense smaller bills. But I do see why someone would find tipping primarily over, say, Venmo preferable, even though I don't think that appeal is enough to outweigh the benefits of cash tips (privacy, universal compatibility, simplicity, etc) in many situations.
Or I could just start tipping everyone everywhere in increments of $20 bills I guess, but I'm not that generous.
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[0]: assuming you did actually mean it as an analogy for dropping cash for digital payments