The format is documented and there are open source "emulators", as well as (many) other Fantasy consoles like Tic-80 and Quadplay that are also open source. Even if you don't want to use Pico-8 for moral reasons, if you have an interest in fantasy consoles, there are many FOSS options. It appears like you aren't really trying, and just complaining about Pico-8. I'm sure you had no problem finding an open source text editor, open source OS, open source compiler, etc. Do some research, or alternatively admit you actually don't care about fantasy consoles or game development, and are here to complain about random software being closed source.