I think the answer to that question is rather simple. Early on we decided on how many conflicts we can create in the time given. As you can imagine WW2 had many different battles and we could only reflect few of them. We picked the ones that we felt portrait best what we wanted this game to be. Since resources are also finite we had to be smart about it. Singleplayer and Multiplayer had to share similar biomes and theaters.
I also wouldn't be too focused on those statements. Not that it's not true, but I think Panzerstorm and the Battle of Hannut (chronological before Twisted Steel and Arras) has shown that we can adjust to the wants and needs of the community. Parts of the Panzerstorm Operation are the consequence of early feedback that the vanilla map offering had to few "massive" battles. :)