What provision would be made for people whose wallet was stolen?
Sometimes you might have just enough cash to get home, or you could rely on the generosity of a stranger. But with contactless payment cards no such arrangements would be possible.

If you forget your Oyster card you are stuck (unless you buy a new one for £5), that seems like a lot for some of the poorer residents.

Buses are an important least cost public transport device and should always cater for the 1% who might otherwise have serious difficulty getting home.

The figure of £24m annual cost is less than the un-used amount on Oyster Cards recently estimated to be £30m per year. For this reason the £24m annual cost of cash payments seems a reasonable cost overhead and a tiny percentage of the overall revenue generated by TfL from tickets.