Because it's generally been borderline impossible to force a large national government to do something better. It's legitimately easier a lot of the time to force a multinational corporation to change than the government.

Since the TSA is generally a federally controlled agency, you'd have to elect a majority of the House/Senate/Executive to change policy there to make it better, and literally no one will run for those offices with even a minor part of their platform being improving the TSA. Even if they had a position you liked about airport security, would you be willing to look past a difference on something like gun laws or school funding or environmental issues to vote for someone who was going to make the TSA more effective? If your answer is no, that's why people have no real hope that the government would improve the TSA.