"It is run frugally and transparently" is a dubious claim, at least according to claims made on NRKs Folkeopplysningen (a show like Penn and Teller: Bullshit, just better). The fund spends a lot on being actively managed, one manager received ~$60 million in bonuses in 2010. However, they won't reply when people ask if bonuses are actually financially beneficial. https://tv.nrk.no/serie/folkeopplysningen/KMTE50009215…
I'd venture that at that scale you don't really have much of an option except going active. Passive is essentially swimming with the stream, but what if you're big enough to affect the stream...you're kinda active in a way already right there.
For assets traded on an exchange at least (e.g., not directly-invested real estate), it's more of a logistical problem than anything else: how do you track indices that you want to track by dripping money into and out of the market, both trying not to affect supply/demand too much, but while not deviating from the index too much. It's the same problem that a BlackRock or Vanguard face but at slightly smaller (!) scale, and one more for computer programmers with knowledge of market microstructure than people that demand outsize bonuses who think they have "alpha" and get lucky (or not).