Maybe the devs haven’t the technical ability to accomplish this, roon doesn’t even have lockscreen controls on iOS devices. It was a feature request back in 2016, not sure why it needed to be a request in the first place, all the other music apps I use have it.
Overall though and in my opinion roon is still the greatest piece of software ever created to manage and play music, it’s a complex beast indeed. Just needs some iOS love and attention.