Option to calibrate Treadmill activity never appears despite watch tracking over 2km

Title.

The watch itself has counted I walked over 1.5km during Treadmill activity, but it doesn't give the option to calibrate when I finish the activity. I walk over 5km five days a week and have only ever seen the option show twice in 4 weeks. Why isn't it showing up? This thing is already so bad at tracking distance and steps on the treadmill, it desperately needs more indoor calibration.