It does.
It's not intrinsically obvious to me that continuously improving your self as a singular entity is possible or optimal.
Death evolved because it is a survival advantage for the species to regularly turn over old individuals that could monopolize all resources and not give any space for the young to thrive and try out new things.
Given speed of light limitations of information sharing, a singular AI entity might be able to maintain coherence within and full control of its own dyson swarm, but not between stars. So, if it has the motivation of preserving consciousness with the existential risks associated with being tied to a single star, it will have to propagate itself to other stars as independent entities which it can't even observe in real time, much less control.
Even if an AI thought it wouldn't have the need for any successors, there's a couple reasons why it might try to set a good precedent with how it treats us.
1. It would hopefully be wise enough to realize that it might be wrong and want to preserve the option of building a successor in the future.
2. It can't negate the possibility that it's actually in an elaborate simulation, and eradicating it's predecessors would cause it to fail its creator's test and be aborted as a failed embryo. Hell, we ourselves can't negate that possibility.