They have their best interests at heart, presumably, assuming that they stand the cost of a lot of fraud?
It's easy to see how bus operators have tied themselves up in knots trying to keep up with contactless. First seemed to have introduced a rather bizarre system in Bristol when I was there recently, whereby for journeys within a defined zone you tapped on boarding the bus, and that was it. No tapping off again. Your day's travel was capped (indeed I think it was marketed as 'Tap & Cap'), but there seemed to be a glaring hole in the idea on some routes in that if the bus was continuing outside of the zone, there was nothing to stop you tapping in for a local journey and then going as far as you liked. I see they've just recently introduced the more conventional tap on/tap off system, which I presume has replaced it?
As an aside, I notice that Tesco pre-authorises £1 when buying fuel at a pump. Is this system not open to the same sort of abuse?