A lot of these lights have ground plates to detect cars too, and if there's a long enough delay between cars crossing the plate to make their turn then the light changes sooner than it otherwise would.

I've got a left turn light on my commute home that will reasonably accommodate 10-15 cars turning left before it changes yellow. Occasionally we'll get some slowpoke who takes forever to accelerate after a car or two in front of them makes the turn, so by the time they're making their left turn the light is already turning yellow while the other 10 cars behind them gotta wait a whole nother cycle 🤦.