A PLOS ONE paper says, The Polar OH1 optical heart rate monitor can be used instead of an ECG device, but why is no one doing this?

https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0217288 Is this because of the arguments we listed here in our journal? Exercice physiologists as Dr. Evan Matthews from Monclair Sate university use chest straps to do exercice physiology with it. Introduction to Exercise Physiology by Dr. Evan Matthews from Monclair Sate university: Polar Chest Strap Heart Rate Monitor demonstration by Dr. Evan Matthews …