Marcus Aurelius' predecessors did not decide not to have their natural born children inherit their estates, they did not have any natural-born children. That's about all there is to it. Of the Antonines only Marcus Aurelius and Lucius Verus had natural male issue. Lucius Verus' son died young, and in any case Lucius Verus died before Marcus Aurelius. Nerva, Trajan, and Hadrian had no children at all. Antoninus Pius, who adopted Lucius Verus and Marcus Aurelius, had at least one daughter Faustina, whom he married to Marcus Aurelius--to Faustina Antoninus left his estate, suggesting that if he had other issue they did not survive him. Antoninus Pius adopted Lucius Verus at the same time that he himself was adopted by Hadrian, as Lucius Verus was the son of Lucius Aelius, Hadrian's initial heir who had died young. Marcus Aurelius was adopted because his father was Antoninus' wife's brother, and his father's premature death made an adoption opportune. There's not much more to be said on the subject. By contrast, Marcus Aurelius had rather a lot of children, many of which survived into adulthood. There was never any question of Commodus' succession.