The idea of approaching and landing on a planet at light speed is clearly something that is considered insanely dangerous. It seems like most people don't even believe it's possible, until Han agrees to try.
It's been well established over the course of the movies that Han is an extraordinary pilot -- he constantly does things with the Falcon that are not normal flight maneuvers. (Piloting the asteroid field, for example). So for him to risk just himself and his one ship on the attempt is worth the risk.
Risking the entire fleet trying to pull off the same stunt is a bad idea; for starters, every ship has different maneuvering characteristics; it's not even clear every ship could make that landing safely. And even if the ships were technically capable of it, it's not something you'd want pilots to try for the first time en masse -- if they screw up, the Resistance loses it's entire remaining fleet and the First Order wins.