Just wondering about the allocation of planes for the LHR-SFO-LHR route.

Last August I flew BA284 SFO-LHR and it was a 777, with the 380 on the BA286.

Currently in the schedule it is a 777 on 284 and a 380 on 286.

At some point in October/November they switch, and the 380 goes on the 284 and the 777 on the 286.

Im booked on 284 in February and would prefer the 777 but it shows 380 (although my app does not confirm my seat number unless I click on booking details.

What is the reason for swapping rotations, and are they likely to change again?