It never used to be that way. Before the terminal came to tables your card used to be taken away and your bill + tax would be settled. You'd then be given a copy of the receipt to sign, and you could add a tip of your choosing by writing it into the receipt and you'd also indicate the total after tip.

This meant that you didn't need to be present when the server would see what tip you'd given them. That awkward moment where they try to not react negatively to a low tip, and try to politely but not overemphatically react with a gracious thank you for a good tip.

That awkward transaction of the tip now happens in person and although I've gotten used to it, I preferred that this was a private moment that the server had after you'd left the table.