Because you currently can't edit blocks.

Correct mister dark_samurai.

(sias oida, hob schon länger nix von dir kheat. Wia schau ma aus mit'n training?)

GED would be very powerfull with a block-edit- and Texture-Tool (incl. Material/Shader Edit).

it wouldn't be too hard to represent the level blocks as entities and write them into the wmp I think. It's more that it could slow everything down on bigger levels.

But creating blocks in GED, maybe with some snapping/painting features for easier use, would be really powerful.

i'd work on the .wmb instead. Its pretty easy to edit anything inside the .wmb format. For editing blocks you would create them in GED, texture them etc, and then you can open up the .wmb, find the 'bsp_blocks' list and edit the position, texture flags, light flags etc.

This is going to be something i might consider implementing in my own editor, although i don't really understand the value of blocks? Shouldn't we always use models?

The blocks are the easiest method to have a decent static lightning.
Thats why they are still useful. Especially for indoor scenes.

For outdoor levels they are pretty much replaceable with
models.