First off, welcome.
Several reasons:
- makuta can survive in space, at least for a little while, due to their nature. Botar, however, cannot. Being in space is different from being underwater, you can’t just hold your breath. Maybe Botar could teleport there, drop his prey, and leave before he dies, but it’s a big risk.
- you can’t teleport through the shields of Karda Nui, unless you have an olmak or warp space like Artakha.
- makuta can teleport too. If botar or brutaka sent a makuta to space, they’d just come back.
- Botar is still vulnerable to being attacked, as we see when Icarax kills him. If the makuta was incapacitated, maybe Botar could take him, but the only one that go incapacitated was icarax. Aka the one that had killed Botar. I doubt his replacement is eager to go for that, even if he could.
- would they even know space is there? These are people who spent most of their history in a world of domes, and only recently discovered the outside world. The only time we see them talking about going into space is in the Kingdom, where they spent several millennia outside the MU.
- In 2008, Brutaka is busy with several adventures and has a broken mask, and Botar is dead and the Order is scrambling for a replacement. You don’t send a newbie after a Makuta.
- Abandon the universe you know for one unknown
- Find a world where the people want a complete stranger from another universe to rule over them
- And also no one in that world has taken advantage of the people’s willingness to be ruled by whoever and already rules.
- And also hope the Brutaka of that world, if there is one, either goes along with this, or you manage to defeat someone who is literally just as powerful as you are.
- Even assuming he does succeed, someone could try and stop him. There is still another olmak in the prime reality, albeit in the hands of the Makuta at the moment, and there is also a great being who can find dimensional travellers and freeze the world around them while imprisoned in a tower on Bota Magna.
Dark Mirror Tuyet was willing to try the whole “find a world where they want you to rule” idea because she had the Nui stone, she already has great power. She also knows how to subjugate a people already, having done so once.
I think the easiest answer is that they only managed to make one clone, perhaps due to time or resources.
But here’s a crazy idea: what if they DID use them all? What if there have always been multiple people going around being called Botar, and they just avoid each other so you never realize there are more than one? All Icarax did was kill one of the Botars.
Of course, none of this is canon, but i think it would be the most fun way to write it. But then you still have the question of why Axonn doesn’t recognize the new Botar.