The Torah in Exodus 12:46 teaches us the prohibition of breaking a bone from the Passover lamb:
בְּבַ֤יִת אֶחָד֙ יֵאָכֵ֔ל לֹא־תוֹצִ֧יא מִן־הַבַּ֛יִת מִן־הַבָּשָׂ֖ר ח֑וּצָה וְעֶ֖צֶם לֹ֥א תִשְׁבְּרוּ־בֽוֹ׃
It shall be eaten in one house; you shall not take any of the flesh outside the house, and you shall not break any of its bones.
Why do we not break the bones of the Passover lamb?
Is it because it was a pagan practice or because of something else?
Sefer HaChinuch #16 explains breaking bones was the way of the poor and at the table of the seder we act as free and wealthy men (e.g., reclining)
For it is not honorable for the sons of kings and the advisers of the land to drag the bones and break them like dogs. Except for the impoverished among the people and the starving, it is not a proper thing to do this.
The Rambam in More Nevuchim 3:46 further explains the Israelites left in a hurry and had not time to break bones
In the same way as the Israelites were commanded to eat unleavened bread, because they could prepare it hastily, so they were commanded, for the sake of haste, to roast the lamb, because there was not sufficient time to boil it, or to prepare other food; even the delay caused by breaking the bones and to extract their marrow was prohibited the one principle is laid down for all these rules, "Ye shall eat it in haste" (Exod. 12:11). But when haste is necessary the bones cannot be broken, nor parts of it sent from house to house; for the company could not wait with their meal till he returned.
