As you install more and more apps, battery life will go down. This will happen on any phone. If your battery life has gone down more than it should is hard to say since it depends on how you use the phone
I could be one app. The more apps you install, the more likely it is that you install one that use a lot of power. It might not use all this extra battery by it self but it can keep other apps or functions in the OS active. Usage that might not be visible in the battery usage overview. There are so many things that can cause battery drain.