I do not see any reason, other than short-term speculation (or the dividend income being necessary) to hold BAM now, given that you can own the same BAM company (plus the extra business) through the parent BN at a significant discount.

A reason could be that owing BN may not necessarily translate to 75% ownership in BAM.

As at December 28, 2022, Brookfield Asset Management's 412,201,980 total issued and outstanding Class A Shares represented a 25% interest in the approximately 1.65 billion shares of the asset management business, with the remaining 75% held by Brookfield Corporation. Of this 412,201,980 issued and outstanding Class A Shares 317,850,364 Class A Shares represented the public float.
bam.brookfield.com - Brookfield asset management announces establishment normal course issuer bid

Above doesn't say BN owns 75% of BAM.

It says BN owns 75% of the asset management business and BAM shares represent an ownership stake in the remaining 25% of the asset management business. It sounds like the actual asset management business is an unlisted entity with 1.65 billion shares.

This may not make a difference as things currently stand, but could in the future if BAM uses its shares for acquisitions. This will result in current BAM share holders diluting their stake in the asset management business to less than 25% but also gaining ownership in the acquired company. BN shareholders will continue to own 75% of the asset management business but will not gain ownership in any BAM acquisitions. The paths may significantly diverge depending on the number of acquisitions. They mentioned non organic growth as a possibility in last year's investor day presentation.