Because Settle the World is still far from beeing a finished game.
Every user can download the "Early Access" game here for free. I know that itch.io is not working for most of the Amiga browsers.
Until the game is ready, I want to keep the (already enormous effort) as low as possible for myself.
Multiple download options for users mean more work for me to keep track of everything and keep all ReadMe files, etc. up to date.
I create the game on my own and, besides my real-life job and family, I have very little time, which I mostly use for programming, bug fixing, and communicating with users.
To give you an idea: when I release a new version of Settle the World, it takes me a whole day to update the ReadMe file and the changelog. I have to create update texts in Itch.io. Facebook posts have to be created and news reports have to be created in all relevant forums, sometimes including screenshots, AmigaLive, AmiKit, Amiga-News, and Amiga Magazine have to be informed...etc., etc.
That's already a lot of work, and when I read through the upload instructions for Aminet... max. 78 characters per line, no HDF upload possible... then that's something that puts me off a bit at the moment.
https://wiki.aminet.net/Uploading_instructions
I would need someone to take over the social media part for me... ;-)
Later, when the game is finished, sure, I can upload it to the Aminet (or earlier, if someone (you?) can help me doing this.