How stupid they are; there are a lot of different campaigns, and they could participate freely.
Now you're assuming they don't have many more accounts in these campaigns already 
I've been thinking about a new data project for a while: once in a while someone finds the same address that is posted by different users, and I assume they find those by searching for that one address. How fun would it be to list all addresses ever posted on Bitcointalk, and add all usernames that posted it to each address on the list?
It'll be a lot of data to process, and I'm a bit afraid the resulting list will be very long with many false positives and many already handled cases. But I'm pretty sure this data will bust a lot of alt accounts 