I guess from a non London-centric view, it’s not an issue. It’s like any other small contactless transaction with no receipt, of which there are many, many, millions.
The specific travel usage thing is that sometimes, the system gets it wrong. sometimes through user error, sometimes through system error, sometimes through no real error, just circumstances. The ability to track back your journeys and the charges for each segment is very useful in that event, I don't think it is possible for an unregistered card.
Of course, as an official old fart (60+) I am a beneficiary of the Boris Bribe, and I get free transport in London, any time. Which is crazy, as I can use it to go to work, the fact that I would do anything to avoid it (even cycle! in London!) is immaterial, but hey ho.