Any number of reasons.
The phone only draws a fixed amount of current when you plug the charger in. If it's using more current than that, there's no current left to send to the battery, so the battery doesn't get charged. That could be a hardware problem (a short or a leaky capacitor) or a software problem (too many apps drawing too much power).
Someone who has more knowledge of cellphones than you do has to have it in hand to determine what the problem is - there are too many possibilities - some of which you probably wouldn't be able to check - to troubleshoot it online.
09-10-2015 08:32 PM