im not 100% on this, but i think it has to do with the bailout from the nrl. as part of it, the wests tigers logo and branding are guaranteed to go on, and i think that this is because the club as a whole has borrowed $8m, and pretty much given up the rights to change to magpies.
again, not 100% on this, but i think that when north sydney was removed from the northern eagles jv, manly possibly took on all financial responsibilities without the nrl, thus allowing them to change the name back.
i think this is the case anyway…