Overwatch is ending hero pools for most of its players. The hero pools, which started on March 7th, have always been controversial. Players disliked losing their favorite characters and were discouraged by their least favorite characters not getting banned enough.
Blizzard has decided that hero pools don't add anything to low SR games. The hero pool system was implemented to make players more adaptable and diverse in the number of team compositions they played. Blizzard states that the reason this is unnecessary in low SR games is that the team compositions are very diverse. Lower SRs are more of the Wild West when it comes to strategy than the upper tiers.
Overwatch is Ending Hero Pools for Most Players
Right now hero pools are completely disabled in competitive. Once the next update is released, they will apply to Masters and Grandmasters games. There has been no date announced yet for that update.
The hero pools are not completely gone though. This week's hero bans will still effect Overwatch League games and the hero pools will continue to affect the Overwatch league. However, the hero pools in the Overwatch League and in competitive play are currently set to be different because the most played heroes are different.