Luffy's flammes are different from sanji's
He needs friction and can't keep the flammes lit as long as he wants
Sanji can do that, post ts he doesn't even need to move because his "passion" is just that strong
Besides, we literally saw king perform a Diable Jambe like attack this chapter and it's similar to sanji's, he doesn't need to move around, he just bursts into flammes at will