The reason we haven't set it to exclusive is that we do allow affiliations to a certain degree, e.g. if somebody is running a small org with his friends but still wants to join the player pool of a larger organisation such as ours. No harm in that.
However, once people affiliate with multiple large organisations, which might conceivably get into conflicts of interest later on, things get complicated. So that's where we draw the line. It's not a perfect system (because the affiliation system in itself is rather half baked from CIG's side), but as long as they don't introduce a middle ground we are closer to open than to pure exclusive.
"Build a man a fire and he'll be warm for a day. Set a man on fire, and he'll be warm for the rest of his life"
Just one further thing to add to the above note, this is point 2 under the "What is your stance on multiple Organisation Membership?" section of our Manifesto on the RSI website:
2. LAMP will only accept members being in orgs with no possible conflicts of interest with us.
-> Social/cooperative orgs like Convoy, PACK, Pitchfork are ok. Orgs with your friends are ok. Pure LAMP sub-orgs are ok.
-> Orgs with their own agendas that might lead to split loyalties are not. As a rule of thumb, most Orgs >50 members fall into this category