The people who want to cast love spells on celebrities tend to be people who don’t have any idea about how real magick works, or the way to do it. They’ve never heard of concepts like the Sphere of Influence, and think that all they have to do is find the right spell and the celebrity that they, and millions of others, lust after, will suddenly show up at their door, even though they have never met, and live thousands of miles away.
Celebrities are human and can be influenced by magick, but it is a lot harder than throwing magick at the girl down the block because, as a celebrity, they have people throwing energy of all kinds at them every day. A lot of them feed on it, and are empowered by it, and are thus immune to most spells, particularly love spells. When you have millions of people lusting after you, like Emma Watson and Brittany Spears do, a love spell from some schmoe in Buttfuck, Nowhere, ain’t going to even cause a ripple.