Because any real fixed wing drone operator needs to know live in-flight data, ground speed, wind speed, heading, GPS location, etc. You don't leave things to chance when flying something you spent a lot of time and money building. This stuff is all available off the shelf and is being used by thousands of people in the US, no engineering on my part required. And I'm not doing anything new at all, I encourage you to go to rcgroups.com and check out their thread on the X-8 Skywalker platform. There are hundreds of videos from around the world from people flying my platform with great success.
The on screen display also gives you real time data on how much juice your motor is using, how much you have left in your batteries, altitude, and its all recorded so if you have a problem you can play it back to try to figure out what went wrong with your system
I am new to all this and would rather have a successful first flight than a crash costing me thousands in equipment. So I learn from others and try to take every precaution against failure. It has taken me years to get this far, and though some have tried to get me to rush into things to serve their own interests, that is the last thing I would ever do.