I thought most of the existing engines out there were too complicated, so I wanted it to be easy to use. Probably that's also why it became that popular.

For a modern engine today - I think the architecture of the engine would look different - and would focus more on creating and organizing content then mostly on rendering.

I was involved in 3D back then wenn Irrlicht & Co had some traction:

Todays graphics engine look completely different than the first flexibel pipelines around 2002-2005, and the rise of AI for usage during rendering will change the tech paradigms further (for the younger ones: In 2001, NVidia announced the Geforce1, we had 1 pixel shader and 1 vertex shader :-D LOL)