Also how many failed expeditions do we know about? Surely not everyone who tried crossing actually made it.
No, because there's no evidence that it happened, the claim is based on hearsay, and isn't even that clear in the claim.
Variations of this question are asked quite often:
See:
https://www.reddit.com/r/AskHistorians/comments/a55gdf/mansa_musas_father_abu_bakr_ii_abdicated_the/
u/Commustar and u/Mansamontezuma do a good job on this in these posts -- and I wrote a bit about it in another answer which I now can't find.
The long and the short of it is that the story is at best third hand (the chronicler al 'Umari says he heard it from Ibn Amīr Ḥād̲j̲ib, who was said to have heard it from Mansa Musa) , it's unclear, written down decades later and as a commentator puts it, Mansa Musa's story may be a "front for Musa to cover any intrigue he used to gain the throne."
So no, there's no evidence that there actually was such an expedition beyond a story.
Columbus had sailed a great deal in the Atlantic -- to the Azores, to the Canaries, and to Madeira. He had noted unknown trees that landed on these islands, blown in from the West. He read a great deal about geography, and as the biography attributed to his son Ferdinand states, he
was impressed by the many fables and stories which he heard from various persons and sailors who traded to the western islands and seas of the Azores and Madeira
There's no sign that Columbus knew of Mansa Musa's tale and indeed that story wasn't even understood to be a claim for a trans-Atlantic voyage until the 20th century. There's no evidence for a Malian or other African exploration of the Americas. There are claims that Polynesians sailed to South America-- not impossible but there's no evidence for it. Recently we've had claims that Chinese may have sailed to America-- again, there's no evidence for that. So far as we know, the only pre-Columbian landfall by anyone other than the ancestors of today's native Americans that is well established by archaeology and historical traditions are the Vikings.
See:Levtzion, N. “The Thirteenth- and Fourteenth-Century Kings of Mali.” The Journal of African History, vol. 4, no. 3, 1963, pp. 341–353.
and
Bell, Nawal Morcos. “The Age of Mansa Musa of Mali: Problems in Succession and Chronology.” The International Journal of African Historical Studies, vol. 5, no. 2, 1972, pp. 221–234.
. . . for a good description of what is known of Abu Bakr and Mansa Musa, the Arab historians through whom these stories come and what we're able to discern of the complex dynastic politics of Mali as we understand them through very limited historical sources