I don't think LE wanted to use all of their 'trump cards' at once. They proably thought releasing the image of BG and a snippet of his voice/audio in February 2017 would be enough to generate tips and lead to an arrest. When almost 6 months went by with no arrest, they then released the composite sketch in July 2017. It may have taken many months to interview witnesses, check alibis and surveillence/SM/bank records etc. before they felt confident in that sketch. For some reason LE lost confidence in this POI/sketch in early 2019 and switched gears. Releasing "Guys", along with the new sketch and video helped re-new interest in the case and generated many new tips, plus it may have been a message to the killer, letting him know that LE does in fact have more information from the recording...and making him stress/guess just how much more they have. If no arrest has been made by the 3 year anniversary of the crime I wouldn't be surprised if LE releases a little bit more audio/video to keep the case from going cold (hopefully it won't get to that point).