My SPG account balances (over 1m points) is not visible from Marriott's side. All I see are my Marriott points and historical activity on Marriott hotels.

I guess, they only had a little under 3 years since the transaction was approved back in 2015 by both board of directors... I work in M&A and our first and foremost goals as we execute transactions is "seamless integration from the client's perspective"

It appears that Marriott's approach is slightly different :-(