Research Assistant has been awarded to 68 individuals which is the minimum of all the badges including the gold badges.
Why is it so? Is it hard to earn?
As it is much more exclusive than the other Gold Badges, why isn't it a Gold Badge?
If having good quality Tag Wikis is beneficial for the site, and is what this tag seems to encourage, then why aren't there more such elements (badges, greater rep) on SO that work to encourage the same?
As this badge has been earned the least, it may be that there isn't sufficient motivation/encouragement for users to make good quality Tag Wikis*.
*Yes, this is not the most important part of the system, but it is important nonetheless.