https://upbit.com/service_center/notice?id=5134
On May 19, 2025, the Upbit South Korean crypto exchange included XEM in the list of cautious trade, and deposit services were temporarily suspended. UPBIT conducts a detailed check of the digital asset to determine whether to extend, lift or ultimately terminate trading support.

I think, most likely the main real reason for the decision was the insufficient from the point of view of the exchange, the volume of bidding XEM.