You haven’t read enough posts.
TRUST LEVEL 3
Get to trust level 3 by…
Must have visited at least 50% of last 100 days
Must have replied to at least 10 different topics
Of topics created in the last 100 days, must have viewed 500 topics
Of posts created in the last 100 days, must have read 20,000 posts (both starting posts and replies)
Must have received 20 likes, and given 30 likes.
Must not have received more than 5 spam or offensive flags (with unique posts and unique users for each, confirmed by a moderator)
Must not have been suspended (including forum suspensions or in-game account actions of any Blizzard game)