The reason the soundtrack for A Better Place is only on Steam right now is because itch would currently require me to make a brand new project page for it. I'd much rather have it as a DLC-style-thing like with Steam. There seems to be a sub-product system being developed (https://itch.io/blog/105823/return-of-the-itchio-changelog-markdown-sub-prducts-...) and I'd like to wait for that to come out and see how it works, and make the decision of how to get the soundtrack here after that.
The reason ALitS has the soundtrack on Steam and itch is because it just comes free with the game.
In the mean time you can listen to the ABP soundtrack on YouTube: https://www.youtube.com/playlist?list=PLaf72QlWgB6ed4_U-jCt43w6IjIjGdyGr