We are warier about being detected. Bystanders are more cynical. We don't want to seem too earnest. These days, we tend to think of all praise as flattery. We rarely bother trying to distinguish between the two.
Praise seems to have become a subset of flattery.
Flattery has never been a flattering idea, but now our slightly jaundiced, strategic view of it has tainted ordinary praise. For one thing, we all have a looser, more skeptical relationship with the truth. We are all moral relativists these days. The Enlightenment idea of truth as a supreme value has gone by the wayside. Nothing is completely straight anymore.