Showing this sort of result in testing is a much harder proposition. It's easy to say that you tested a feature or product that made $X over a time frame of Y years, but lets be honest here: being the product manager or lead developer and making the same statement definitely carries more weight when attached to a resume. The person generating the idea and the person originally implementing the idea will always be seen as being closer to the end result and positive cash flow than the person ensuring the value of the idea, and ensuring that the mass market can actually use your idea as expected. I'm not saying that this is "the way things should be", I'm just stating it's the way things are.
That being said, here's why I think demonstrating the value you've directly provided to a product is harder for testers: you can't show the diff between what the product would have made had the bugs you found been released to the public. That is an alternate reality we don't have access to; it's an A-B test that can't be run.

If it were possible to conclusively show that the company made $Z more because of the bugs that had been found, I think testing would be taken more seriously across the industry.