Pretty sure Clippy is trademarked. Had the same idea but did not go through with it because of the TM.
Trademarks have to actually be used to remain enforceable, I think. Not sure MS could claim Clippy after all this time, not that they might not try.
Three fact that it's not a product anymore doesn't mean it's unused; a quick search says they at a minimum used it in 2021:
https://www.microsoft.com/en-us/microsoft-365/blog/2021/07/0...