The two main reasons I see that tip percentages have crept up is the social pressure to not be the one that tips "poorly" and that automated prompt with suggested tips.

Those end up in a feedback loop. If you're standing next to someone and the tip options are 15, 18, and 20 percent, there is a social pressure not to tip the lowest amount. It's the same where if there are 3 wines on the menu, the cheap, the reasonable, and the expensive. Most people won't buy the cheapest option. The cheapest option is there to pressure you into the middle one. Well, now that they have that, why not slowly increase the suggested amount to 18, 20, 22. Or like we are seeing in a lot of places now. 20, 25, and 30.

What sucks is that there are no repurcussions for businesses that suggest these larger percentages. Nor are there any for businesses that traditionally are not tipped to display the screen as well. Not until we either pass legislation to regulate tipping prompts or collectively refuse to purchase services from these businesses.