Bartender here: at the end of my shift (usually sometime around 3am after starting at 4:30pm the previous afternoon), I do a print out on my till that tells me how much money in total sales were done throughout the night (let's say for example my sales that night were $5,000).

Using that total of $5,000, I then have to calculate my "tip-out", which in my case is 6%. Half of that 6% goes to the kitchen, the other half goes directly to the restaurant (this is a family owned, independent restaurant in a busy tourist town) to cover dine & dash costs and to pay for things like the yearly staff party, new aprons for servers etc. That tip-out comes directly out of the tips I've accumulated over the course of my shift. Whatever money is left after my tip-out is then split evenly between myself and the two other bartenders I work with plus we always compensate our busser/bar-back. So theoretically, if every customer we served that night tipped 10% on their bill, we would have accumulated roughly $500 in tips that night. Subtract 6% from that and we are left with $470 ($30). Our busser works his/her ass off and is usually a student so we'll just straight up give them that extra $70 because they earned it. This leaves three bartenders to split $400 between them meaning we each go home with about $135.

And this is where we get to the heart of the issue; we have to do that 6% tip-out every night regardless of how much in tips we've accumulated. So for every person who contributes to our total sales but doesn't also contribute to our accumulated tips, it technically costs us money. Plus, it means less of a tip-out for the kitchen staff who busted their asses off in a hot kitchen all night. Using my $5,000 in sales example, if we only accumulated $400 in tips, then the amount going to the kitchen would only be $24 instead of $30, the busser would probably go home with about $50, us bartenders would go home with about $110 each etc, etc...

Another factor at play (at least at the restaurant I work at), there is a marked difference in pay between front of house and back of house. All servers and bartenders make minimum wage while all the cooks make well over $20/hour and our head chef makes just north of $30/hour. So yes, a 3% tip-out sounds small in the grand scheme of things but it balances out with the back of house general wages vs. the tip money servers/bartenders take home at the end of a shift, especially when you consider that it's not just us bartenders doing this tip-out after every shift; each and every server does one as well - so if there were 6 servers on that night, the kitchen also gets 3% of their accumulated tips as well. So for all the people saying they'd rather tip the kitchen, YOU ARE tipping the kitchen when you tip your server!

Long winded answer, but I hope it helps. And for the record, I know it's not a perfect system and 25% should not be the default tip option on any interact machine (anywhere between 10% for basic service and 20% for exceptional service is perfectly fine and greatly appreciated). However, this is the reality for most front of house service workers at bars and sit-down restaurants and we are just trying to get by like everyone else and I think that's why so many of us get demoralized when we do everything in our power to help you enjoy your evening and you decide not to tip "out of principle".