Photoshop Mobile Not Working with My Current Plan – Why?

I have an Adobe Creative Suite subscription for PC, which includes Photoshop. Recently, I installed the Photoshop app on my phone as well, but the app won’t let me log in. Instead, it asks me to purchase a separate subscription to use it on mobile. I don’t think this is fair, so I wanted to ask if this is actually how it’s supposed to work, or if there might be some issue. What confuses me even more is that I can use Lightroom on my phone with the same subscription, but not Photoshop. Why is there a difference?