Spending a billion dollars take a lot of effort (or so I assume; I've "only" spent millions). People will ask annoying questions like "where is the billion dollars coming from, I had no idea you were a billionaire", and ask about AML etc.

Conversely, driving down the value of a company that's already worth billions is "easy": Just publicly demonstrate your willingness to drive the company totally into the ground.

Or if you want speed, and have access to the funds, the super-fast way would be transferring a billion worth of crypto to a random address.

For my part, my biggest "losses" were paper values in startups that failed or didn't get the exits we'd hoped for. There it's also "easy".