I wonder where testing and QA measures fall short on these massively popular applications such that they become slow and bloated over time. Is it the case of ma

I wonder where testing and QA measures fall short on these massively popular applications such that they become slow and bloated over time. Is it the case of management seeing actual metrics and not caring? Or does it become harder and harder to find such issues due to increasing legacy device/library/code support (even for companies like Snapchat and Facebook!)?