Public information in such things are unreliable.
But even if true, IU in her music and branding is far more independent, than BTS is.
And good for her, if she negotiated a better deal than BTS did.
Nevertheless BTS having a smaller portion, still has a far larger pie to take from, than IU does.
Being a soloist also helps, BTS might have trouble retaining the name 'BTS' if they broke away from Big Hit. Rebranding is not an easy thing at all - Beast/Highlight?
There is no guarantee that BTS will do better independently of BigHit, so why spoil a fantastic thing?
And being stakeholders in BigHit/Hybe means that they will continue to profit from future acts, starting with TxT, Enhyphen etc. Whereas EDAM has no such future. Of course I do think IU would have a bit of Kakao M as well.
In any case, the business skills/deals of idols are utterly irrelevant compared to their artistic skills.
Well frankly it would be an improvement if fans even considered art, given their fixation with visual and trivial.