Just NO. Quite obviously you are drawing wrong conclusions from what you have seen and don't actually know what you're talking about, bro.
Ren'Py is one of the most easily customizable game engines in existence. You are obviously drawing a wrong conclusion from how few of the Ren'Py games have customized UI's, but the fact is, that since Ren'Py already by default has a rock stable UI, an excellent save and load menu and well working other menus, game devs can just concentrate on creating the
game content and they have
no need to waste their precious time on building custom menus from scratch for saving, loading and changing settings of the game. In fact they have no need to learn much else than the very basics of programming to create VN type games with multiple and meaningful choices and paths. And a lot of them actually have no previous programming skills and little idea how to change the default looks of Ren'Py UI.
This is why most Ren'Py games have similar or identical UI's.
Changing the looks of Ren'Py UI is just a tiny bit more difficult than writing some very basic game script for it, there is definitely no need for any "superior technician capacity"
. It's not html/xml nor css, but anyone who has ever learned anything about them, gets his (or her) head around it pretty quickly, should they only bother to study those default configuration files a little and read a bit of Ren'Py Wiki.
There is no need to build the UI from scratch in Ren'Py, the looks of the default one can be changed
a lot without any skills in Python. But it also doesn't mean that building it from scratch is more difficult than, lets say for Unity or some node-based engine or for the engine that Palmer's team has modified for their needs.
Most of the other engines with some exceptions are not so generous and devs
have no choice but to build all necessary menus from scratch. This is why they all look so different - not because it's easier for the devs to customize them, but because they have no choice.
BTW, I am in no way trying to justify the idea of porting this game to Ren'Py.