What happens if you put a 64bit executable in a container they try to run the container on a 32bit machine? Or a Rasberry/Arm device?
When you try to run an executable on an architecture it wasn't designed for, it does not run. But this has nothing to do with docker or Linux.
This, by the way, is the reason we artificially prevent docker from running on multiple archs. If half of the containers you download end up not running on your arch, and there's no elegant way for you to manage that by filtering your results, and producing the same build for multiple archs (and what does it even mean to do that?) - then all of sudden using docker would become much more frustrating.
This sounds like a clothing manufacturer who only makes clothes in black because trying to match colors would be too frustrating for customers. At the end of the day, lots of people have multiarch networks, and don't want to have to choose between using a tool or supporting just one platform. Removing functionality does not make their lives easier.