My Galaxy Watch5 is registering regular steps and distance acurately.

However, I just started using a treadmill.  The watch is measuring my heart rate and the time (when I set it to "treadmill workout" in Samsung Health) but it does not recognize the number of steps or the distance.

I did put my phone in my pocket today and my phone registers the steps on the treadmill and then syncs with my watch correctly.

But I don't understand why the watch doesn't track my regular walking vs. on the treadmill automatically.