There could be several reasons. Maybe your privacy settings are set to 'private' so only specific people can view it. Check your settings to make sure you haven't accidentally restricted access. Another possibility is a glitch in the app. Try closing and reopening the app, or even reinstalling it.
Well, first, ensure that you haven't muted your own story. Sometimes we accidentally do that. Also, Snapchat may have some temporary issues. It could be a server - side problem. If that's the case, you just need to wait for a while. And if you have recently changed your account settings related to who can view your content, double - check if you've made it too restrictive. For example, if you set it to 'Only me', obviously no one else can see your snap story.
It might be due to your network. If your connection is poor, it could prevent others from loading your snap story. Also, if you have been blocked by a large number of your followers, it may seem like no one can see it. However, the most common reason is still the privacy settings. Make sure you have the right audience selected for your story.