If they don't want to come, don't push. They'll not only ruin your good time if they're not having fun, but you won't hear the end of it.

Leave them behind, then tell them about all the fun they missed out on. Maybe they'll change their tune for next time.

I would guess that the reason the resorts tell you its not safe to leave is they want you to stay on property... you might spend money in the spa or elsewhere... captive audience spends $$$...