This is an informal opinion poll with no immediate mandate for action to be taken.
Yes, users from other teams could create a separate account to earn Gridcoin with, but 10 years of team loyalty discourage this practice. Imagine endorsements from linustechtips or teksyndicate because their teams could begin earning gridcoin, imagine a dramatic reduction in censorship across multiple websites.
The figures from Boincstats do not break the stats down enough - users in a team includes both active and inactive users, there's only 8.38% active BOINC users, it's highly plausible that these active users have a higher percentage of team membership.