Force carb question

I'm on my second round of root beer. First one went well. Did enough research to get a good understanding. I'm running 30' of 3/16 at 30 psi for carbing and serving. This second batch is getting super foamy all of the sudden. Any good guesses? Second question is why can't you force carb at 30 psi and when it's ready being the psi down to like 5 psi which should give youthe ability to run a shorter serving line.

Because over time your root beer will lose carbonation....all the way down to 5 psi

Its more annoying than disasterous, to slowly lose pressure that way, in that you have to push it back to 30 every few pours.
I do this with my kegs since I don't have a dual manifold or splitters.
I still use a longer line in those cases anyways though, so I'm not sure on the short line part.