Hi Archtek!
TLDR: I DO hope to release the game on Steam.
Steam has a lot of hurdles, is more complicated and has more gatekeeping than Itch.io. I picked Itch.io as my initial launch platform because they make it so easy to post new builds. They also have a more flexible cost system for developers. Right now, Masteroid doesn't even have an installer, you just unzip the files and play. Releasing on Steam will require me to improve my build process a lot, have installers and patching systems, and do some things like getting an Apple signing key that have a direct cost in both time and money. These are important but take away from the feature development focus I have right now!
Purchasing the Itch.io game gets you access to all future updates on Itch.io for free. My hope is that when/if the game does launch on Steam, I issue a free key to all Itch.io purchasers. However, I don't know Steam's restrictions or costs to developers well enough. If it costs me more time and money to issue a steam key than players paid on Itch.io in the first place, I will probably not offer free Steam keys.
Hopefully that seems reasonable and fair! I do my best to deliver the best quality I can to gamers and fans!
Thanks for posting,
Justin