Black holes do not technically "suck" light in the way that a vacuum cleaner sucks in air. Instead, a black hole's immense gravitational pull warps the fabric of spacetime around it, creating a region of space called the event horizon. Anything, including light, that crosses the event horizon of a black hole cannot escape its gravitational pull.
While light is indeed massless, it still carries energy and momentum. In the vicinity of a black hole, the intense gravitational field bends the path of light rays, causing them to follow curved trajectories. As light approaches the event horizon, the curvature becomes more severe, and the bending can become so extreme that the light's path becomes directed inward, towards the black hole. Once inside the event horizon, the gravitational pull is so strong that even light cannot escape, and it is pulled towards the singularity at the center of the black hole.
It's important to understand that the behavior of light near a black hole is a consequence of the curvature of spacetime caused by the black hole's mass, rather than an interaction involving the mass of light itself. The gravitational field of the black hole affects the geometry of spacetime, and light follows the resulting curved paths dictated by that geometry.
In summary, it is not the mass of light that causes it to be trapped by a black hole, but rather the extreme curvature of spacetime caused by the black hole's gravitational field.