Samsung Pay is pretty good - I've just switched from Google Pay because I brought a Galaxy Watch Active2. It's not as straightforward to pay using your phone, but it prevents other people from just dumping your phone on a reader to pay for stuff.
In terms of putting Google Pay on Samsung's watches, they probably won't because Google Pay's designed for Android/Wear OS and Samsung's watches use Tizen - Google probably wouldn't write an app if Samsung asked them because it's a competing (and IMHO, better) platform to WearOS.
I got a galaxy watch active 2 but my bank doesn't support Samsung pay (NatWest). there is a work around though. if you sign up to curve (free) which is supported by Samsung pay you can link your bank card to the curve card. so I use Samsung pay on the watch through curve and the payment comes off my NatWest card
I bank with Nat West. I don't particularly think its a good effort by Samsung at all. I have just upgraded to the S21 Ultra where I also believe they are doing away with support for Samsung Pay. So if they are not supporting the S20 series they need to provide an alternative.