Why does working an early shift make someone so tired afterward?

My hunch is that you did not get 8 good hours of sleep before getting up to go to work. You can test this yourself.

Shift outside the hours of 6am-7pm can cause shift work disorder. It makes you tired due to loss of sleep hours and loss of circadian rhythm. If regular early mornings tire you, take a rest during the day . Sleep habits impact brain functions. Limit your caffeine intake to < 400 mg/day. Exposure to blue light suppresses melatonin, charge devices outside the bedroom. Hope this helps.