building webpages is easy, you just need to code it using html then put some php in it then use CSS to style the font,color and design.
while building apps for android took a lot of time, you need to understand gradle and other framework. so it times consuming, not to mention your computer need to be high-end to achieve better functioning apps. and also you had to convince your user to install the apps and also need to enable push notifications. many user forgotten they had install any app until they get push notifications on their phone. in conclusion, building apps is useful but not as useful as webpages that can run on anything.