This question is asked since the the source code was released a few years ago.
Microsoft wanted to demonstrate their XNA game development environment and used the old MC2 code as example (MC2 was never developed under XNA but was ported into it for demo purposes) .
Microsoft's priority was not to support MC2 fans.
Therefore they took out or deactivated a few features because a public release of the related code was potentially against their interest.
The third party BINK video was taken out/deactivated for legal/commercial reasons ( no video anymore in MC2 mods).
The multiplayer code (mainly everything that lets you make network connections) was taken out for security reasons and continued use elsewhere (no more multiplayer).
Since these are rather complex topics to re-implement and the MC2 community is microscopic (because I created maps for a league some years ago I know that MC2 Multiplayer was NEVER big) it is not the priority of remaining coders creating MC2 mods