Jefferson was selected to draft the declaration of independence because

"When the Second Continental Congress convened in Philadelphia in 1775, it was far from clear that the delegates would pass a resolution to separate from Great Britain. To persuade them, someone needed to articulate why the Americans were breaking away. Congress formed a committee to do just that; members included John Adams from Massachusetts, Benjamin Franklin from Pennsylvania, Roger Sherman from Connecticut, Roger Livingston from New York, and Thomas Jefferson from Virginia, who at age 33 was one of the youngest delegates.

Although Jefferson disputed his account, John Adams later recalled that he had persuaded Jefferson to write the draft because Jefferson had the fewest enemies in Congress and was the best writer. (Jefferson would have gotten the job anyway—he was elected chair of the committee.) Jefferson had 17 days to produce the document and reportedly wrote a draft in a day or two. In a rented room not far from the State House, he wrote the Declaration with few books and pamphlets beside him, except for a copy of George Mason’s Virginia Declaration of Rights and the draft Virginia Constitution, which Jefferson had written himself."
(Jeffrey Rosen and David Rubenstein)
Web site: https://constitutioncenter.org/blog/why-did-jefferson-draft-the-declaration-of-independence

Hope this helped