I was in Bangkok last month. Riding the BTS I heard the recording in English that went something like this. The Health Ministry has said wearing masks in open areas is no longer required. The BTS "RECOMMENDS" wearing a mask in the BTS Train. Never did they say it was mandatory. I think you need to read between the lines. No masks in open areas but inside the BTS Train is an enclosed area. Why the recording didn't say it is Mandatory to wear masks I don't know.