I have an external hard drive that I had to format in ExFat because I was using both a Mac and a PC at the time. When I plug my Ext HD on my Samsung Smart LED LCN40 it says there are no videos to be played. When I plug the HD on my LG 4K it reads every content inside (except mp4's, apparently LG have a problem with it...but it does play mkv perfectly).
What's the catch? Does Samsung have an issue with ExFat format? Or is it the fact that the files are inside folders so that's why the tv claims there are no videos to show?
Why are you making the assumptions that TVs has to play videos like able to play from any HDMI source?
TV abling to play videos from a USB storage or via LAN is implementation dependent and not something any vendor promise you. Even TV of the same vendor but different model may not give you the same capability. This "video feature" is just something they throw at you to wet your appetite, to sell you the TV, rather than a serious feature, IMO, with lots of limitations.
Limitation such as why some limit you FAT/FAT32 only and not let you use something more robust such as ExFat or even NTFS which is been around forever.
Limitation such as MP4, MKV blah-blah, these are "containers" you have probably heard the term, is really what's the inside codec being used is what matters. With a PC, if it can't read a certain format, you just load the proper, missing codec and BAM! can't do that with a TV, none TV that I know of, and TV vendors don't promise you anything about what video codec they support, heck they don't even tell you that in the manual.