Are you a web developer? This may be more your speed.
You know all those tests that your developers are meticulously maintaining? They're probably not testing the requirements that you care about.
I mean maybe some of them are, but a lot of them are what are called 'unit tests'.
They're testing software interfaces, not human interfaces. They are not testing the full functionality of your website.
That doesn't mean those tests aren't worth writing, they absolutely are. It just means they may not catch the bugs that you care about. And the tests that catch the bugs you care about are the hardest to write and maintain. They are called functional tests. To be frank, your engineering team probably hates writing them, so they probably don't invest all that much energy in making them comprehensive.
In many organizations, QA is solely the responsibility of the engineering department. But let's be honest, nobody ships truly bug-free software, and the number one product requirement, before any feature, is that the platform works. So bug testing is a responsibility that we should all share. By relegating the responsibility of product quality to the engineering department, you end up with a lower quality product and more divisive finger pointing.