why can’t i use the pip3 that comes from windows in wsl2 ubuntu?

To use pip3 on WSL-2 you need to force using the “.exe” binary on your command line:

pip            pip.exe     pip3         pip3.8         pip3.8.exe     pip3.exe
^ not work     ^ work      ^ not work   ^ not work     ^ work         ^ work

You will also need to install Python under Windows beforehand.