because ask @caithleen about it, I can tell you that the nether isn't supposed to be there, nor the end, etc etc because reasons, also, it's because you don't NEED AN OXYGEN TANK! that's why! if the world doesn't require an O2 tank, you're REALLY not supposed to be there
Well if you got a tardis, all the oxygen worlds are your reward. Thoo theres not sooo much to do when you are there. Mainly exploration of the worlds and the tardis mod.