Wasted space on Blu-ray discs?

[Datalyss]

Rather than try to explain, I'll examplize:

Let's take my 2 disc editon of Transformers 2007, and let's forget for the moment that movies on BD supposedly look better when played on a Blu-ray player. Disc 1 is the feature film, and disc 2 is the special features Now, I checked Amazon for Transformers on Blu-ray. It's also on 2 discs. WTF? Surely there is enough space on a BD for both the film and the special features. I mean sheesh, a single-layer BD is 25GB, and it''s 50GB for a dual.

Is it this way for all movies on BD? Cuz I would think the studios would take advantage of the extra space, and put everything on as few BDs as possible.