¯_(ツ)_/¯
I don't think I've done anything particularly special. I post every weekend on Sunday at midnight, so old readers are probably familiar with the schedule and know when to expect a new update. Otherwise, I just try and reply to every comment. The Webtoons readers seem to really appreciate when the author 'notices' them (a few have literally thanked me just for replying to them, which I find kind of cute)
I also let them know ahead of time if I'm going to miss an update because of school, and they've been really understanding. (Hell, a ton of them wished me luck on my midterms, and they're currently waiting on me to finish my finals lol)
In any case, I do think the system is the main reason for the drop for most people, but it's best to just keep doing what you do and people will come naturally if they enjoy the content.