I doubt if anyone knows, but the supply chain for those models has been wonky since Thanksgiving. They were out of stock at several places, then they came back in stock at ridiculously low prices (five dollars per sensor in some cases) then they went out of stock again.
Typically when an item is marked as still being carried but out of stock it means either that they are selling out altogether or there will be a new model coming out soon. But nothing’s been said officially.
Amazon is now showing both the contact sensor and the motion sensor as “only available from third party sellers,” which usually means Amazon itself is not expecting new stock to come in. But is that a model change or EOL? No way to tell.
https://www.amazon.com/Samsung-SmartThings-Door-Window-Detector/dp/B077JRX1PW
You can check with people in the following thread and see if anybody has heard anything recently: