I often do, indeed I often leave a drink behind the bar. Why should the wait staff get all the tips when the person who has actually cooked my food gets nothing?
Three good answers to that:
1. Your tip is how you hold the staff accountable for good service. To hold the kitchen accountable for good food, you send the food back when it isn't good and the restaurant eats, pardon the pun, the cost of that
2. You pay for the food in the prices on the menu.
3. They generally get a cut of the tips. The same isn't true when you give the tips to the kitchen instead of the wait staff
4. Cooks get paid a higher hourly rate/salary than does the kitchen.