Number of bugs can grow super-linearly while their impact might be decreasing preserving the overall usability increases. Basically as your software grows there

Number of bugs can grow super-linearly while their impact might be decreasing preserving the overall usability increases. Basically as your software grows there's more corner cases that will get tested very rarely if ever. Number of possible states grows almost exponentially with code size, so it would be very weird if the number of bugs grew sub-linearly.