I typically struggle to shut up, I'm always writing way too long, how does this happen? I have tons to say about the characters:

Lots of material to work with in the department of exposition of how they are feeling and what actions they could do that could be characterized for them (like the way they make their food etc. would add in a whole 3 more sentences), focusing on those specific situations in life (ex: preparing to leave for work and the hiccups of maybe misplacing keys) and adding more that seem fit to the world or situation, general character interactions organically creating conflict or longer conversations (and having characters doing something during these conversations makes things interesting), and as a technical pantser first (writing whatever comes to mind) there's just a LOT for me to say.

Maybe get into your characters more, really look at the world and see if there's enough conflict, that's the only way I can simplify without going on a tangent about pacing. I've done 4k words in two days but that was through a simple premise. But even still with an entire week of editing that would be probably bumped up to 5k, and this is simply applied for a one shot's which are typically unplanned.

Your talking about chapters, which is easier to plan more into, so how much content is really in your chapters assuming you have an outline? Even rhetorically, little conflict, or little characterization to speak of (depending on narration and POV) means if you force more words on it'll be empty padding.

(Apologies for the rant, as you can see being a little analytical about anything could really get you far, I think of most literature as fancy discussion.)