Very few Starwood properties were still owned by Starwood when Marriott took over.

As of 2016, Starwood only owned 24 properties, and a few, like the Sheraton Centre Toronto and Tremont Chicago, have since been sold.

https://s1.q4cdn.com/483583335/files...List-Final.pdf

They had already been selling properties for years, and managing them under long-term contracts with the buyers, I'm sure Marriott intends to sell the rest.