פירוש על עבודה זרה 124:7

Abaye says that the baraita does indeed mean that the workers are paid in sabbatical year produce. As to the objection that sabbatical year produce cannot be used to pay debts, Abaye says that they find a permitted way to give it to him. He draws an analogy with second tithe, which also may not be used to pay a debt. One cannot say to his fellow that if he helps bring the second tithe to Jerusalem, where it must be consumed, he will share it with him. But he can say that when they bring it to Jerusalem, they will eat and drink together. So too with regard to Sabbatical year produce, he can give it as a gift to his worker.

When it comes to the instruments buried with the executed people, everyone will know that these items are prohibited and will not come to dig them up. But with the individual burying the wheat that he gained through renting out his ship, people might think he is burying it just to hide it because he stole it. Then they will come to steal it, which seems fitting since they suspect him of being a thief. To prevent this, it must be burned.
As an aside, it seems far more likely that people would come to try to steal the sword for it is more valuable. But rabbis never executed anyone so this source is not so “realistic.” Burying the sword is a symbolic act, not meant simply to prevent others from benefiting from it. On the other hand, the story of the wheat seems to be more realistic.