This is due to multiple factors including being unaware of how long we're hyperfocusing for, and neglecting other important factors. I've made a video on ADHD Hyperfocusing, the common issues it brings to those of us with ADHD, and some helpful tactics to keep Hyperfocusing on check and not let it take over your day/schedule.
If you're interested, the vid is uploaded on my ADHD Youtube Channel. Link to my channel is in my bio description on my profile here (you can click my pic to get there). Hope this helps.