What does it mean that Rob ter Horsts scientific results about smartwatch accuracy where not reproduced in scientific papers up to the present day?

Rob ter Horst started testing smartwatch accuracy systematically and scientifically around 4 years ago on YouTube:

But would one not expect 100 papers if Rob tests 100 smartwatches, which he tested up to last year?

But this did not happen. On the contrary. The number of papers about smartwatch accuracy decreased:

Only very rarely, we find a new paper about smartwatch accuracy.

Does this not mean, that Rob ter Horsts test results are not reproducible for other scientists? Since hardly anyone seems to write new papers about this topic. And would not someone do this, if it would be of interest for the scientific community?

But this seems not to happen. An the contrary. And companies like iWorx, Adinstruments, Schiller, BIOPAC, etc. seem to know about this a long time ago. Since are optical heart rate monitors and smartwatches not only a hot topic for Rob ter Horst, but not for these companies?