Causes of downfall of a Man, pointed by Buddha in Mangala Sutta

His mother died after childbirth, and his father was a Sakya clan leader, he didn't need wealth. Filial piety or family commitment wise, all craving must be abandoned, so as sad and irreconcilable that instant is (even though, always, the story of the Taoist farmer is good to remember), it is anyways at some point necessary on the path. Buddha later put in rules that disallowed his own path to a Sramana, such as the parents had to consent to their child's wish to become a monk.

In the end though, the wealth was given away, and as a revealer of Dhamma, as he said to Rahula when he demanded his wage for being his son, the 'only' remaining wealth he had to give was through teaching Dhamma, which he did to him, and to other members of his clan.

Mangala Sutta discusses things which are blessing or auspicious. Parabhava Sutta is what discusses what leads to one's downfall.

We understand this as explained by thee; this is the third cause of his downfall. Tell us the fourth, O Blessed One. What is the cause of his downfall?

Parabhava Sutta

Supporting one's parents is a blessing.

To support mother and father, to cherish wife and children, and to be engaged in peaceful occupation — this is the greatest blessing.

Mangala Sutta

If you are wealthy and having the means and do not take care of your parents this lead to your downfall. This essentially is applicable to householders, though the Vinaya explicitly allows for monks to take care of their parents.

In the case of the Buddha or a monk, one leaves a householders life to seek enlistment and one is living on the charity or alms of others who support you seek liberation. In this case, you do not have the means to support your parents as a householder would do. So this does not lead to your downfall.

The Buddha searched for the Dhamma and found it. When the time was right The Buddha gave the gift of Dhamma to his parents which surpasses any material benevolence he could have given them.

In Anguttara i, 62, the Buddha said that even if one should carry his mother on one shoulder and his father on the other shoulder for a hundred years serving them dutifully, one could never repay them. But if one could incite one's parents to practise generosity and morality and establish them in faith in the Triple Gem and wisdom, one does repay what is due to one's parents. Among the Ten Subjects of Right View, understanding that there are results of one's actions (kamma) towards one's mother and father constitutes Right View. Therefore, one should always hold them in veneration in one's thoughts, speech and action.

TEN BASES OF MERITORIOUS ACTION

Among those following is the one among them; 1) Those who have ample wealth does not support his old aged father and mother has a downfall!

Philosophy aside, just by going with plain simple logic and there's no contradiction here. The statement and the premise is clear: those who have ample wealth who do not support their aging parents will face downfall. The Buddha and His noble disciples did not have ample wealth and hence did not satisfy the condition for the downfall. Now including the philosophy, one can safely say that what the Buddha did at the end for His parents, siblings, son, their many relatives, and countless many people was an extraordinary kind of support no other worldly support was able to match:

"I tell you, monks, there are two people who are not easy to repay. Which two? Your mother & father. Even if you were to carry your mother on one shoulder & your father on the other shoulder for 100 years, and were to look after them by anointing, massaging, bathing, & rubbing their limbs, and they were to defecate & urinate right there [on your shoulders], you would not in that way pay or repay your parents. If you were to establish your mother & father in absolute sovereignty over this great earth, abounding in the seven treasures, you would not in that way pay or repay your parents. Why is that? Mother & father do much for their children. They care for them, they nourish them, they introduce them to this world. But anyone who rouses his unbelieving mother & father, settles & establishes them in conviction; rouses his unvirtuous mother & father, settles & establishes them in virtue; rouses his stingy mother & father, settles & establishes them in generosity; rouses his foolish mother & father, settles & establishes them in discernment: To this extent one pays & repays one’s mother & father.” ~~ AN 2.32 ~~