Let me try to explain it again. Jeramiah was specifically addressing:
Jer 17:19 Thus said the LORD unto me; Go and stand in the gate of the children of the people, whereby the kings of Judah come in, and by the which they go out, and in all the gates of Jerusalem;
Jer 17:20 And say unto them, Hear ye the word of the LORD, ye kings of Judah, and all Judah, and all the inhabitants of Jerusalem, that enter in by these gates:
Specifically addressing "the kings of Judah" and all that went in and out of the gates of Jerusalem. All inhabitants of the country known as Judah.
In context, Jeramiah is addressing a certain issue, sabbath breaking, that the inhabitants of Jerusalem were doing.
So what is a "burden"? The word translated "burden" is:
Massa = “burden”
1) load, bearing, tribute, burden, lifting (noun masculine)
1a) load, burden
1b) lifting, uplifting, that to which the soul lifts itself up
1c) bearing, carrying
1d) tribute, that which is carried or brought or borne
2) utterance, oracle, burden (noun masculine)
3) a son of Ishmael (noun proper masculine)
The proper definition here is probably "tribute". One commmentator says:
The country people were in the habit of coming to Jerusalem on the Sabbath to attend the temple service, but mingled traffic with their devotions, bringing the produce of their fields and gardens with them for disposal. The people of Jerusalem for their part took Jer_17:22 their wares to the gates, and carried on a brisk traffic there with the villagers. Both parties seem to have abstained from manual labor, but did not consider that buying and selling were prohibited by the fourth commandment.
In other words, the people were coming into Jerusalem to worship on the sabbath and were bringing MORE than just their offerings with them. They were bringing extra to sell on the sabbath and had made the sabbath into a day of commerce.
You're laboring under the misconception that the orthodox Jewish definition (non-scriptural) of "burden" is the correct one. This is the same view that the Pharisess had who had made the sabbath a burden by their manmade rules and regulations.