Mea culpa, I should have added '...in my jurisdiction'. (Norway)

I haven't looked into the legal background, but my guess is that offshore workers' unions have lobbied for it - and, most likely, it only applies to flights to/from sites operated by major players.

Also, some countries refuse to recognize training from other countries (Brazil, I am looking at you!) - so you end up having to do the same basic training in [n] jurisdictions, having [n] different certificates on you at all times, all with their individual refresher requirements...