How to explain this ? Oh, I know... Imagine that both Ren'py and Unity are car's building kits.
With the Ren'py kit you have tons of motors, seats, windshields, steering wheel and in fact tons of everything needed by a car. But you have only one "base" on what you can build your car. So each piece can only be put at their given place and whatever how unique your car will be, after driving few cars made with this building kit, anybody can drive anyone of them. They know where "this" will be, how "that" will works and so on.
In the opposite, you've Unity. It's also a car building kit, but instead of tons of motors, you've tons of screws, bolts, small metal pieces, etc. You don't choose which motor you'll use, you build your own motor, design your own gearbox, and in the end you put everything in whatever place you want. So, each time someone want to drive a car made with this building kit, this person need to relearn how to drive.
Reported back to the subject, with Ren'py you know where to find the variables and how to address them. And like the base is always the same, you also know how to do it. But with Unity, the variables can be everywhere. Each single value in the memory space used by the game can be, or not, a variable. Obviously each one can be found and changed, but to achieve this you need to make a new tool specifically for each game.
And this, simplified explanation is why you can't have an unRen-like tool for Unity.
