Simply put, distance.

Gravitational force is proportional to each mass and the reciprocal of the distance between them squared.

So with a black hole, you can get a lot closer to the center of its mass than with a star. If you lose half your distance, you feel 4X the gravity. Since the sun is almost 1.4 million km wide, and a black hole of the same mass would be tens of km wide at most, we can get a lot closer to the black hole. Orbiting 50 km away from a 1-solar-mass black hole (near the event horizon), you would feel almost 200 million times the gravity that you would on the surface of the sun. From the same mass.

The math is more complicated IRL (always is).