Using Uber and Lyft is like going into a bar and never tipping your bartender. You'll get a drink the first couple times, but after while you may notice it get's harder to get the bartender's attention for your next round.
More and more ridesharing driver's are taking a star off passenger ratings for not tipping. They also look at passenger ratings as part of the decision process for accepting your ride request or not. The lower your rating goes, the harder it's going to be for you to get a ride.
If there are no issues with my ride, I always tip my driver. I really wish Uber would change their app to accommodate including the tip on my charge card.