According to the Koran, every Moslem must visit the Ka’aba once in their lifetime. It is a must-do. So they will go to comply
Only if they are well enough and can afford it. Even at this years rate of 3 million Muslims at the Hajj, at most a couple of hundred million could do the Hajj in one person's complete lifetime. this means that just for space reasons only a small fraction of the current 1.57 billion Muslims will ever be able to go.