To the best of our knowledge (and I did email itch.io's support about this) getting the game on discount shouldn't block you from getting a Steam key. They did mention that some people have their Steam account and itch.io account attached to different email addresses and that can cause problems, but unfortunately that's not something I can help troubleshoot. Here's their troubleshooting page on Steam keys to double-check, and if that doesn't help then I suggest emailing support (there's a link to that in the final section of the troubleshooting page).
And thank you for the praise! Hopefully you can get the key matter solved on your end, but we're grateful you'd even consider buying the game twice 💙