Bus lanes are great when they are in force, but for some unknown reason, outside peak hours, a lot of bus lanes revert to general traffic lanes. Which means that a motorist can drive in them, and park in them.
However, most motorists don't use bus lanes at any time. Partly it's because with all the other street clutter, they don't notice the signs giving the hours of operation. Partly it's precautionary, so they don't accidentally get a ticket when they didn't read the hours of operation, or the current time, correctly. And very rarely, it might be out of concern that a cyclist might be using the bus lane.
As a result, you get an empty bus lane that is an invitation to aggressive drivers to undertake. "The other cars should be in the bus lane", they reason. "I would be overtaking them on the right if they were where they should be." I've seen this behaviour many times. It's common on the Morden Road in Merton, and I've seen it on South Lambeth Road approaching the Vauxhall Gyratory. This kind of undertaking is potentially lethal. It's often done way in excess of the speed limit, and the speeding car is hemmed in by the traffic in the other lane on one side and the pavement on the other, so has no chance of swerving to avoid a cyclist. Sight lines are often poor, so the driver may not see a slow-moving cyclist at night on a wet day until it's too late.
I've never quite figured out why all bus lanes aren't 24-hour. It can't be parking demand. Most businesses are closed by 7PM, so there's no great need for customer parking or loading. Parking restrictions in side roads often end at 7PM in any case. Residents won't habitually park in bus lanes because they come in to force earlier than most people will move their car in the morning.
As far as traffic flow is concerned, outside peak hours, a single lane gives enough traffic capacity to avoid congestion, and if it didn't you'd need to enfore the bus lane to avoid the buses getting caught up in traffic jams.
The justification put forward for not having 24-hour restrictions on the bus lanes on CSH7 is that the CSHs are for "commuting cyclists". As if no-one commutes after 7PM. But here's the paradox. In commuting hours, speeds are usually lower and there are plenty of cyclists around - being noticed isn't so much of a problem. The time a cyclist most needs a dedicated lane is at night, when visibility is poor, motor traffic speeds are higher, and there's less 'safety in numbers'. This is also the time when there's less demand for roadspace, so it should be easier to provide dedicated space.