Why do the poor have to give away their wicker baskets yet the rich get back their gold baskets and I know the Gemara says this proves that wealth goes to wealth and poor goes to poor but why IS THE halacha structured that way?
I have always understood (and I believe this is written in one of the standard commentaries - possibly - רע"ב) that the gold baskets were more considerable to their owners because they were expensive and therefore were expected to be kept after their purpose was served, while the straw ones were expendable.
The Mishnas Yaakov on the Rambam (Bikkurim 3:8) by Rav Yaakov Nissan Rosenthal, says that he heard from the מהגר"י כהנמן זצ"ל that the reason the Kohanim keep the poor peoples' baskets is because they prepared it specifically for the mitzva of Bikkurim. Since as they were weaving it, they intended that the basket be used so that they could complete the Mitzvah properly. Therefore the basket itself also becomes part of the Bikkurim. Rich people don't make their own baskets so the same thing doesn't apply.
Rabbi Frand, in this article, writes that the Malbim on the Passuk says that the Kohen keeping the basket is a merit for the poor person, because he had to actually gather the supplies and weave the basket himself, unlike the rich person, who just went and bought one.
The legal principle behind the law of the bikkurim basket is the concept of bittul, “nullification.” If object B exists solely to serve object A, and has no role or identity aside from that service, then B is regarded as an extension of A. The straw baskets of the poor are thus “nullified” to the fruit that they hold, and become an inseparable part of the gift. Not so the gold and silver vessels of the rich man’s bikkurim. The materials and the workmanship invested in them impart to these baskets significance and identity all their own, apart from their role to hold and transport the bikkurim. Thus, when the first fruits of the farmer’s land are elevated to the domain of the kohen, they do not draw their container along with them.