While I cannot speak for the op I would guess a few things might be the service is on a whole different level in Koh Samui than Vieques. The breakfast cannot be compared either.

While Vieques is laid out with many rooms close to each other in blocks and mainly just rooms, Koh Samui is a Villa only property and every room has a pool.

You have 2 restaurant choices in Koh Samui and only 1 in Vieques, same goes for the bar situation. (Discounting pool bars at both)

There is nothing wrong with Vieques, but I think it is completely accurate to say it is not on the same level design, service or food wise as W Koh Samui and for anyone unaware of how these things can differ it is good to draw attention to that so people can go with the correct expectations.

I should add I do like W Vieques and will return, but having been to it several times and also Koh Samui multiple times I fully get where the op is coming from.