The process is anything but simple at large companies. Even if the new hire is a complete fraud and can barely write code it'll still take an average manager 6-12 months to be able to show them the door. And it'll involve countless meetings and a mountain of paperwork, all taking away time from regular work. And then it'll take another 6 months to get a replacement and onboard them. That means your team has lost over a year of productivity over a single bad hire.