I say again, it's sheer laziness on the part of BA's schedulers. They simply can't be bothered to plan ahead. Much easier to do it on the fly, but much less convenient for the pax. It's the same thing at Gatwick.
You really think that an airport can run with stands being allocated “on the fly”???
Stands show in the system at least 48 hours in advance!!!! They frequently change to BA’s requirements and as necessary due to delays of outbound and inbound flights.