Maybe it's because the IG app on laptops doesn't have the feature to watch stories. It's mainly designed for mobile devices.
Well, it could be that Instagram has restricted the viewing of stories on laptops for technical or security reasons. Or maybe they just want to encourage more mobile usage.
The inability to watch IG stories on laptops might be due to compatibility issues. Also, IG might be focused on optimizing the story experience for mobile platforms to ensure better performance and user engagement.