Statistically speaking there will be a few percent of bad hires and people whose skills don't match the requirements. Arguably, they could detect that during probation period, possibly extending probation period needed. That's how it's done in more progressist european countries. It gets harder to fire people after that.

Note that they also routinely fire perfectly capable people, who exceeded expectations for many years in a row and just had one bad year (sometimes after a team change or a promotion).