I know you might not be allowed to discuss any details, but could you try to explain in general terms why the legal situation for expansions is so much more complicated than for the main games?
Just speaking from my professional experience, it could be a number of reasons why it's more complicated, but it all boils down to GoG and EA not wanting to expose themselves to possible litigation from some party they forgot about if they go ahead and release the expansions. Quite often, stuff like this isn't necessarily done by the same devs and EA or GoG needs to go back and check to make sure that they do indeed have the rights to distribute these games digitally. Another thing to keep in mind is that many of the agreements EA has on file with these devs were signed by people who are probably no longer with the company, so things need to be triple checked to insure nothing was left out when the agreement was originally inked and everyone with rights to the content comes out happy in the end.
EA in all likelihood has/had a boilerplate agreement with their devs who have worked on core games saying that once the game has been released, EA retains the right to sell or distribute it however they choose to. Sometimes, considering the age of these games, those agreements lack any kind of language in regards to whether or not EA can rightfully distribute said works digitally or what EA can do with subsequent expansions, since those are often based upon a whole other agreement. So it becomes a huge gray area and the legal research process on that end can take months. Basically, they want to insure themselves no one will get litigious if they go ahead and release the expansions.
Also keep in mind there might be some kind of agreement EA had in the past with previous devs that amounts to EA retaining all the rights to core games, but will allow devs to have a greater profit share or control of expansions and other content, etc.
Granted, this is all speculation and I'm basing most of this off of my own professional experience in another industry as well as anecdotal accounts I've heard from friends within the industry about matters like this. Take it as you will.