Every physiology is at least a bit unique. As George Sheehan always asserted...."we are experiments of one."
Henrik, his older brother, was flagged by WADA on the fancy bear website for doping.
Norwegian skiing is rife with PED use - it is everywhere on the internet.
Jakob is a phenom in a gene pool not known to produce any unlike Kenya and Ethiopia similar sized populations that have uncountable running prodigies.
The explanation here is obvious.
That's what I wrote above.