Indeed SQ for a very short window of time allowed all its passengers to use the Privium West Lounge,
(off peak travel)
Currently only SQ elites: PPS club get access per invitation only. Otherwise LKY would rise again!

I didn't know about Etihad, thank for mentioning !
Also an interesting insight by you, that by moving the entrance direct next to elevator / stairs : lounge surface can be increased.
And extra set of public toilets can be absorbed to satisy the "needs" of the larger lounge.

If i remember prepandemic,
Star Alliance Gold passengers using a different Star Alliance carrier lounge are accounted internally as $35 (now $45),
bill sent to the FFP of their respective Star Alliance carrier granting the status.

So i bet the non-Schengen Star Alliance carriers at Amsterdam,
are only willing to fork out $45 per business class passenger for Amsterdam lounge access:
KLM asking to much,
Privium asking to much,
Aspire undercutting the price to compete on quantity......the only choice left ...

Priority pass might be only offering even less to Aspire so those entering with priority pass / premium credit cards are considered lowest of cash cows ....

But the clear winners are the OneWorld passengers + elite ...
I vote to start a petition that in lieu of the loss ... but in memory of the British Airways lounge,
the new OneWorld lounge should re-introduce 'Chocomel" + "Bifi" in honor of nostalgia !