[TelegramApp]

The main reason is speed. MTProto is designed to work fast on weak mobile connections. Another reason is security, with HTTPs you need to trust more parties.

[veeti]

> Another reason is security, with HTTPs you need to trust more parties.

No, you don't. Use a self-signed certificate that is hardcoded in the app.

[JshWright]

Or better yet, use a cert signed by a trusted CA and pi it in your app.