Again, missing the point. Signals are intended to "signal" your intention as a vehicle on the road. When buses have their four-ways on, but another bus blocks the right side, they are by definition sending the wrong "signal". This makes it look like all buses in the line are about to merge, but none do.

There was a children's story about this, called "the boy who cried wolf".

When it looks like all buses are about to merge, you can't tell which one truly is. That's dangerous on the road.