Bus lanes generally (but not always) have to end before junctions for a number of reasons, including the nature of carriageway markings. Lanes are multiplied at junctions to increase motor traffic capacity, which is generally a bad thing (more motor traffic, less cycling and walking, more congestion, worse air, more noise and all the usual reasons). Left-turn only lanes are generally not advisable, as they tend to increase the number of left hooks on cyclists who want to stay close to the kerb and get overtaken by drivers turning left. Left-turn-and-ahead lanes are vastly preferable.
Bus lanes generally (but not always) have to end before junctions for a number of reasons, including the nature of carriageway markings. Lanes are multiplied at junctions to increase motor traffic capacity, which is generally a bad thing (more motor traffic, less cycling and walking, more congestion, worse air, more noise and all the usual reasons). Left-turn only lanes are generally not advisable, as they tend to increase the number of left hooks on cyclists who want to stay close to the kerb and get overtaken by drivers turning left. Left-turn-and-ahead lanes are vastly preferable.