they even took the stickman physics

they didnt (you cant just take C++ code and slap it into a lua based code), and the stickmen are probably originating from dan ball's powder game (2007, it is still available at dan-ball.jp)

why make it again???

why not, there are like tens of falling sands(one of the earliest "tpt-like" games and the genre name) games with different features

The Powder Toy is open source and the source code is hosted at github where everyone can copy the code, modify it and start their own version (this is called a fork of the code, and this is how mods are made). If you click on the link you can see that there are 737 forks of the Powder Toy source code at the moment of writing.

TPT is based of the "falling sand game" genre, they aren't the same at all. TPT isn't original either (https://en.wikipedia.org/wiki/Falling-sand_game)

and honestly noita is best one in terms of gameplay

in terms of functionality the best is tpt