> What about when event structures change? Now you’re having to push versions into your events and keeping every version of your serialisation format.

Sure. Events are like filled out forms, and there is a reason forms that are significant, modified over time, and where determining meaning from historical forms is a expected business need tend be versioned (often by form publication date). If you ever need to reconstruct/audit history (whatever your data model), you need a log of what happened when that faithfully matches what was recorded at the time, and you need definitions of the semantics as to how the aggregation of all that should map to a final state. Event sourcing is a pretty direct reification of that need, and, yes, versioning is part of what is needed to make that work.