It wouldn't surprise me if the total number of bugs to be fixed skyrocketed in the past 5-10 years, too. The design and testing phases of the SDLC are nonexistent at most web dev companies and the culture is focused around adding as many new features as fast as possible. With those priorities, bugs wouldn't even be noticed until after they've been deployed, and the later in the SDLC you catch the bug the more expensive and difficult it is to find the root cause of.