I highly doubt money played much of a role in her decision. With endorsements, she will meet or surpass anything she is receiving via NIL, and a lot of those very same companies almost certainly will continue their current contracts with some modifications.
I thought about it a lot last night, and pondered what I would do in her position. Obviously, I'm not in her head, but if it was me I would want my legacy to be 4 years.
I know some are predicting that we won't see an asterisk next to the statistics but my guess is we will on most data boards. I wouldn't want my legacy of amazing accomplishments to (potentially) be tarnished by an eternal asterisk. Those in the know are aware that she accomplished the records in 4 seasons, but that may not be common knowledge 30 years from now.
Either way, she is ending up in the WNBA. Why not cement your legacy at the standard 4 years? With a 5th year she would put those records in the stratosphere, but always hear the, "Yeah, but..."