One thing I've never understood is why we have to shift computer time to match celestial bodies. We have a definition of the second (in terms of a Caesium atom)

One thing I've never understood is why we have to shift computer time to match celestial bodies. We have a definition of the second (in terms of a Caesium atom) and we've agreed on the epoch, so why can't we just leave it be? I understand that if we want to know the time in 'human language' (in terms of the earth's rotation around the sun, and the specific timezone that we're in) we then have to apply these corrections. Surely that's simpler than every timekeeping device on the planet having to adjust a second? Electronic devices are much more likely to be sensitive to a second's difference than us humans are.