Well as Adibordoy said its down to banks, and can always swap to Google Pay and use it across all your Google devices even if it's not Samsung specifically. Like I use Sony phone as well and via Google pay it automatically syncs across without any issues.
It won't with a galaxy watch as Google won't allow it. If you can set up your cards on Samsung pay via Curve then once all set on the watch you can switch to GPay on your phone (if you prefer it).
Try using Curve as that allows most if not all banks and able to add loyalty cards too. Works with all mine including those that don't work with Samsung Pay.
As other users have already mentioned (thanks!), the number of banks available on Samsung Pay depends on the banks themselves, not on the Samsung. Therefore, unfortunately, at the moment, nothing can be done regarding your suggestion 😕.
