What is the weather app doing that it requires 100MB? For such a simple application, that seems excessive.
I think this depends on your location, because in some places you really want to view a radar map. "Rain in $CITY" is practically useless for me. Still, the (static?) map in the depicted app shouldn't take 1GB.
Mostly rendering. A bunch of images, text, UI elements. On a modern high resolution display it adds up quite quickly. You can surely cut it down a bit, but 100MB isn't absurd.