That's a less that deep analysis of all that was going on, but you're entitled to it.
1. I think the legal environment in Alaska made her continuation in office an extreme financial burden, and this is verifiable.
2. I think she had political and financial reasons that were far better handled in the lower 48.
3. I think that there was enough time for her republican replacement to gain the recognition he needed after assuming her seat as governor. IOW, she gave her replacement a huge leg up in the next election...she gave him incumbent status.
Others are free to ignore all those reasons. After all, this is, for the time being, a free country.
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iow...her political and financial ambitions were better served by quitting her elected position.