Why does Garmin penalize me for "biphasic sleep"?

My Epix 2 Pro always reduces my sleep score because I get up in the middle of the night to read and do other things. I then go back to sleep and typically get a good nights sleep. And this is historically how humans sleep before the electric light bulb (biphasic sleep). But my sleep score is always dinged even if I got a good amount of REM and deep sleep.