Because you do not simply stick the plunger in and pop those tabs. They are a force of evil and I even bent my metal tools to open mine.
People replacing the battery be warned, you can buy a battery from China for 17 shipped on eBay, however what this guide does not tell you is one you open it, and re close it, there will forever be a gap on the top and bottom between the mesh and the rubberish spine. I have not since then tested the water proof feature because of this gap. You are warned and he should have warned us as well.