Very few people queue as Tanks since it is not a very popular role to play as due to the high tolerance demand requried for a Tank Player. Healers are the 2nd least played role so it is common for them to get the bonus once in a while but the majority of the player base main as a DPS character.

However, once 4.0 is out we should see more DPS and Healer needed in the bonus again like in 3.0 when so many people wanted to play as Dark knight and Astrologian during the first week.