Then how did he hand over the dice if it wasn't a physically solid projection?
Since we don't know how the projection worked (other than the dice fading away), we don't know the rules. Maybe it can be interacted with, but it's revealed to be an illusion; how would it look if the lightsaber had just clanged off Luke's chest, or passed through it, with a cut that closed up afterward?
It's like asking, once again, "Why didn't they just shoot Yavin in the first movie instead of circling around to shoot the moon, giving the Rebels time to blow up the Death Star?" There is no doubt some reason that it doesn't work on a gas giant, or that the beam would dissipate if they tried aiming it through the gas giant, but we have to accept that in universe there is some reason that the physics of it did not work.