Because when a letter arrives at their doorsteps, James having written the one to Sirius, Remus, Lily, and Harry and Regulus having written Pandora’s, telling them that they’re death eaters and that they’re sorry, it’s a bit of a cause for concern. Especially when those letters are straight to the point, informing them that Voldemort is launching his attacks and that they all should run and hide far, far away. And then Peter disappears, likely working with the dark lord as well...