my assumption is that it was a stylistic choice both, really, but also just simpler to do. link's awakening's room format is object based, and link's awakening's rooms neatly fit into this, being 10x8
every object is just two (or three) bytes: the x and y position are one, then the type itself (and length/orientation). some of lttp's areas are much larger, so you'd need accordingly more memory for that, and the gb at the time wasn't offering you snes-levels of space
there's also the motion blur aspect to consider. movement on the original gb was pretty blurry and fuzzy, so constantly scrolling on move would've left you with a lot of ghosting. focusing on making every room fit into a single screen meant that wasn't as much of an issue.
and, honestly, it just works better. consider the oracle games where every dungeon room is more or less "full size": it's just not as good. you get more space, sure, but now you also have to design around things just not being on screen.
