They offered it early in the game but some players abused the ability to switch between different systems to cheat. So, they've taken it away. If they keep the system, they have to spend extra time to deal with cheaters instead of improving the game or fix bugs.
Q: Will players be able to share, transfer or link Steam and mobile accounts?A: We offered this very early on, but found that some people were using it to cheat. We already spend a lot of development time preventing cheating that could be spent working on features, so we decided to just disable the feature. It’s too bad, as the PC version has some cool stuff. If there’s a way to make this work in the future, we’ll try it.