I agree with you that she does not owe anyone an explanation.
But she made the choice to offer one.
Or rather claim that she was offering one while putting out a statement that is foggy and inconsistent.
Rosa Parks did indeed also offer explanations for her actions.
Parks' explanations were consistent with her previous actions which showed a long commitment to civil rights. No one ever suggested she was hypocritical or self-serving, because she took a brave stand. She did not wait till the busses were already being boycotted before taking her rightful place. Rosa Parks put herself on the line, rather than waiting till it was safe.