S2722QC, 50Hz supported?, #2

I'm really struggling to understand that in this day and age, that 50Hz isn't supported at 1080p or 4K resolutions? All of Europe work at 50Hz?

Most bizarrely, the Dell S2721QS that I have, WILL work @ 25hz? A division of 50? But not 50Hz?  24, 25 30 and 60!?