Why were so many colonists concerned about religious freedoms being protected

Because they or their parents had lost them.

Explanation:

The colonists in the thirteen American colonies were especially aware of the feeling of losing religious freedom because the primary motive for many in coming to the New World was to be able to worship freely.

The American colonies were certainly an economic venture, but they were also a safe haven for anyone who did not fit into the societal structure of the England of the 17th Century.

Groups of protestant christians like the Puritans fled to New England where they would have the freedom to practice their religion without being harassed and persecuted.