Gift cards are thoughtful things.
They're a way of saying to friends and family, 'I know you prefer to pick your own present'. They're a way to put a present to one side, saving it for later when you've made up your mind. And, if you're getting one for someone who you don't know inside-out, it saves you second-guessing what you think they might want.
Gift cards are a surefire way to make certain they'll get something they love.