It's possible you might be giving up more capability by tearing apart the aviation part of the MEU than you intend, or incurring more cost elsewhere. I know amphibious assaults seem far-fetched, but it seems the LHDs provide a platform for organic CAS where you might not have any long runways to operate from, from a place where you might not want to put your carrier strike group (right off the shore, for example), or across a wider area by not being attached at the hip to a CVN (for a lesser conflict where you don't need to tie up a whole CSG). The MEUs can operate within its own expeditionary strike group independent of carrier strike groups, so I guess it could tie up the Marines' freedom of movement or incur the cost of more CVN strike groups to cover them, which gets expensive also.
I guess, in short, you'd be tearing apart the whole MAGTF structure. I'm not an expert on the Navy/Marine side though, so I could be totally wrong; just some food for thought.