Because 95+% of consumers would rather have something simple to install rather than something that requires drilling holes in their house or professional installation.
How is this device powered? Do you have to charge it or is it connected to an outlet in some way?
I'm thinking that you might already have to drill a hole for power.
But presumably the existing doorbell would already have simple wires running inside?
You can either wire it in to an old doorbell for power or you can disconnect it periodically and recharge via USB.