I’ll go with Hollywood crap:
From the wikilink:
Ibn Fadlan reports also what he observed for burials for those not of high status or wealth. He says that when a poor person dies, he is cremated in a small boat built by his fellows. When a slave dies, the dogs and carrion fowl devour the body. When a robber or thief dies, his body is hung on a tree and left there until the wind and rain dismember it.[25]
He then gives a detailed account of the burial he witnessed of a great man. In such a case, Ibn Fadlān says that a third of his wealth is inherited by his family, a third pays for the funeral clothes, and a third pays for nabīdh (an alcoholic drink) to be drunk at the cremation.[26][21]
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I always thought it a waste to bury a ship with the dead (or burn it). Seems like the small burnt boats were makeshift. The wealthy guy probably had other ships, and they used the oldest one that may have been on it’s way out anyway. 15 years old was probably old for back then. Propped up on cinder blocks in the backyard. “Yeah, one of these days when I get around to it I’m going to fix that baby up! That was the first ship I ever owned you know!”