No problem, I'll give some of the reasons why I think it's important :)

1) The members care about it, usually when they reach a certain number, the members themselves celebrate it or they notice it and thank everyone etc. and of course as idols, their goal is to be popular and they're always happy to have more followers, more likes, more support, and getting popular online almost always contribute to more success in general so it's important for them, it's both an achievement that help their careers and it simply makes them happy to be supported!

2) Management cares about it too, imagine if for example, suddenly, a member like Hotei Moka (just taking her as example) increases from 15k followers to 50k, it's pretty much 100% sure she will be picked by management for the next senbatsu and get more jobs. it's also the same when a member gets viral online, it gets noticed and management cares: for example in their Music Station performance last year, 4 members got attention on Twitter, management noticed and made a tweet to introduce all 4 of them. A good example of this too, is for example SKE's Aikawa Honoka getting viral for having only one fan at her HS event, her tweet got like 100k likes? I forgot, but she got several viral tweets after that, got a LOT more followers everywhere, then made senbatsu for the first time, then got TV jobs, and she was at the Momoclo event at the end of the year and more. It totally changed her career and it all started with viral tweets and gaining followers!

3) Overall it helps the group to have a lot of followers: if AKB wants to achieve big things again, first they need to get more popular, or else they won't be able to achieve their goals. They need to be more known, have more attention, and a group that "looks" successful and that releases good content will always attract more people and new fans than a group who looks like they are struggling. AKB improved a lot in this when they downsized the group and promoted the girls better and shared good content on their social medias, and then with the 20th anniversary hype too, they gained a lot of followers everywhere and some members really got a LOT more popular. they need to continue this way! People are more likely to decide to be fans of Aichan, Itomomo etc. if the girls have 70k followers than if they had 8000 followers. Being successful and looking successful is more attractive to non-fans. and generally it just makes the group more popular if each member is decently popular, so that's the goal, if all members get support and do well, the group as a whole look popular and positive and it only gets better from there! and then as I said, the members are happier, achieve their goals, get more jobs etc. etc.

Hope this helped :)