If there is no PS5 or Series X available (we can see PS5 November and December numbers) then it would be hard for them to outsell Series S in the month that whatever is available is likely so sell.
I have seem the USA comments here, and Series S have been readily available for several months already and still wasn't able to make Xbox the best seller.
Actually lack of appeal is the only answer possible, because if it had so much appeal, with it being the only system available it would be selling out instead of being readily available for several months.
You are missing the point entirely. With the Series S being easier to produce due to a more available chipset, they are more readily available and that is why it is selling more. People are more willing to drop 300 bucks on a Series S for now, knowing they will still have it for MS exclusives later on than they would likely be to drop a similar amount for a PS4...a console that is going to lose support in a year or two at best.
Then when a PS5 or Series X is available they trade the S for an X or just buy a PS5 to go alongside the S they already have.