> what is wrong with giving people basically a free coffee or soda or snack on me.

https://dash.harvard.edu/bitstream/handle/1/9491448/Here's-a-Tip_Torfason,Flynn,Kupor-Tipping-and-Bribery-6-6-12-SPPS.pdf

“We suggest that tips and bribes both emanate from similar norms of exchange—indeed, the timing of the gratuity may be the key distinguishing feature between these two acts. This subtle temporal distinction may help explain why tipping and bribery practices are positively correlated across countries even though many individuals perceive them as diametrically opposed from a moral standpoint.”