We are cynical on this too. If you have worked in the service industry you are quite aware that it is overwhelmingly a transaction.
I feel similarly. On our first cruise, we loved our serving team, they were so attentive and friendly. We gave them the envelopes on the last evening, and showed up for breakfast the next morning. The warm friendliness was gone. It was really disappointing. We have stopped giving the envelopes, and we don't do breakfast on the last morning.
This past cruise, we were not really happy with our serving team. They were generally very friendly, but they were so, so slow. They never had our drinks ready for us at the table. It took "forever" to get bread and drinks and menus. The food server always seemed rushed. Even though they told us at the beginning that
DCL was changing the way that they did food service - from a food server and a drink server to just two servers who could do either job, that wasn't true. If we asked for drinks from the "food server", he would tell us to wait for the other server who was better equipped to handle our drink order. The head waiter told us one evening that he was going to prepare a cheese plate for us the next evening - never happened. We didn't care, but it was just the point that he spent time asking us about cheese and telling us he was going to do it, and then he didn't.
They gave the "excellent speech" at least 3 times during the cruise. We always told them that they were doing fine (good/great), because we believed that they were truly doing their best - but, their best just wasn't excellent.
In general, we don't give the excellent ratings. Partly because we think that there is always room for improvement, and partly because we have a pretty high standard for what is considered excellent.