The more famous is the group smaller are the chances of their sales to grown. Seems counter intuitive right? But I'm going to make it clear
Girlgroups generally have much easier time issuing hits. Many girlgroups can debut with hits (BGs almost never release hits at debut), and big GG are very likely to have at least one smash hit at the time of their third comeback. This means at their second anniversary girlgroups are probably approaching very high levels of popularity
This make GG fandoms grown really fast, mainly driven by their music and live performances and not so much due to group side content and activity (reallities, TV shows, concerts, v lives, etc). Case is when a group has a smash hit like Next Level and Love Dive everybody pays attention on them. Their follows up singles while successful do not really present group to any new audience, unless of course the group manage to break a market they don't own already
The boygroups in other hand had a much more limited audience i.e. smaller hits (if any hit at all). More often them not their fandom is built between comebacks, due to online fandom activity
This basically means there are many kpop listeners who likely do not have paid any attention to that group last comebacks. We can clearly see it with SVT, many of their 2020-2021 releases were silent and ignored by a very big part of kpop community to the point many questioned "how have they get so big?". Being ignored means their pool of potential fans is bigger, simply because there are more customers available which translates in fairly high amount of increase in sales even many year after the groups debut
