It wasn’t until 1622 that England established copyright laws and it wasn’t until 1710 that the laws reflect much of what we understand as copyright laws.
The laws were not being relaxed in terms of copyrights, they were being strengthened in 1789 when the U.S. Constitution was being written. Jefferson and Franklin were both strong advocates of copyright laws in the colonies and later the United States.
The original length of copyrights were 14 years with another 14 to be applied for. However, throughout the 19th century, the move was toward more stringent protection of an artists or inventors works. The Constitution was not a loosening of copyright and patent laws, it was a step on the way of recognizing that people who do the work should own the fruit of that work.
And since the United States is a signatory of the Berne Convention now, that treaty has the same weight of law as the U.S. Constitution itself. (You can look that up in the Constitution. Article VI reads in part: This Constitution, and the laws of the United States which shall be made in pursuance thereof; and all treaties made, or which shall be made, under the authority of the United States, shall be the supreme law of the land)
And where is the liberty in taking someone else’s work and making money from it? That doesn’t sound like liberty to me. It sounds like theft.
That's because you've bought into the notion that ideas can be "property".
And, your history doesn't go back far enough. Before the Law of Queen Anne, it was normal for publishers to hold exclusive right, and before the Statue of Monopolies, letters patent were granted far and wide to non-inventors. The Constitution specified limits on who Congress could grant monopolies, which are now flouted with publishers, heirs, executors of literary estates holding monopolies when the author has been moldering in the grave for 70 years, and using them to suppress derivative works (e.g. "The Wind Done Gone" -- a retelling of "Gone with the Wind" from a slave perspective), performances of dances (cf. Martha Graham's artistic estate) or use of poems as song lyrics.
By your reasoning the Fantasia on a Theme of Thomas Tallis, Variations on a Theme of Paganini, and a host of other musical works using other composers' themes as starting points are "theft" (or at least become so if the composer of the new work or an orchestra performing it make money). Rubbish! That's how culture works: it builds on previous culture. Putting a rent-seeking heir or lawyer into the process is contrary to the expressed purpose of the Constitutional provision, to promote progress in the sciences and the useful arts.
Progress in my own field -- mathematics -- would grind to a complete halt if we had to pay royalties to other mathematicians and get permission from them (or their heirs or publishers) to use their definitions or theorems. To not be a "thief" (of honor for originating the idea, not of the idea, which is not something which can be stolen) consists in putting a citation to the paper the definition or theorem came from, and eventually, when the notion becomes well-known enough, even this lapses as the definition or theorem becomes part of the common patrimony of mankind. (Maybe the discoverer is honored with his or her name attached to the result, maybe not.)