1. She failed at putting Yahoo back on the map. She spent billions on acquiring businesses that bring in close to no revenue. Maybe it's a great place to work, but if there's no money coming in, it won't stay great long.
2. She failed at financial engineering; she couldn't even get a tax free spinoff through.
I would've been happy to cut her some slack if she did one of these things right, and messed up the other one. Some people aren't meant to be product people and others just aren't financial engineers. But this is basically throwing in the towel.
Don't forget, this idea of a reverse spinoff didn't come from Marissa. It came from an activist investor, who are basically, master financial engineers.