Avatars could be worn by "Newbie" accounts back then, but they were disabled for security reasons in 2013[1].
Newbies are a lot but limited members will buy the Avatar membership.
Following that, it was re-enabled in 2015, with "Full Members" as a pre-requisite[2]. And I'm guessing there won't be any additional membership fees to wear an avatar because that's why the forum was hacked in the first place.
When it was re-enabled, security problems were fixed. Admin did not re-enable it if problems were not fixed.