Because some people like flavour
Guilty as charged. I would spend an hour or two refilling my Cafe Mocha.
TBH I do not add sugar to anything and wish many sugar free drinks were not loaded with so much sweetener - they are overpowering and taste a little odd. With the Cafe Mocha I was shocked to discover how much sugar was in it - when I looked at the Wetherspoons menu I saw it is the same as the hot Chocolate. It is really coffee flavoured hot chocolate. So reluctantly I feel some sweetener is needed as a replacement.
Potentially but then they might've decided they just don't have the demand to bother. I doubt many people were going to spend all morning drinking hot chocolates, but tea/coffees yeah. Maybe children, but you wouldn't think children would be in Spoons long enough for more than say a couple of them.
Granddaughter would get through a few hot chocolates. Usually when we were out and during late afternoon I would top up her metabolism with chips. No wonder she "liked" the chips !.
I can only think the alternative is chocolate with artificial sweetener even though I dislike over sweetened and/or artificial sweetener.
The way Wetherspoons deal with the regulations is to give you a sachet of chocolate with your order for the initial cup - that allows for the policing that the machine could never achieve. I tried using half a sachet, so as to spread over two drinks, and it just is not good !. There was me thinking I did not have a sweet tooth. Anyway it alerted me to how much sugar was in the (wonderful) thing and I prefer to be sensible.
As for the Wetherspoons hotels. I have noticed a few in attractive places and friends have spoken quite highly of them.