UX pattern-driven tipping pressure is gradually normalizing a "voluntary" (but not really since you are extorted via ratings) layer of non-progressive consumption taxes.

There are now apps and other point-of-sale interfaces which default to 20% for "tips". Nice way to lower labor costs by outsourcing a voluntary fee to your customers, but this mostly destroys the signal/feedback value of the tip and rating.

Do the nudge crowd know they are engaging in semantic pollution, e.g. diluting the value of the data they are spending millions to collect, process and analyze.