Why Do All Superheroes Need Secret Identities?

Throughout the history of superheroes secret Identities were a core staple of the genre. Clark Kent and Superman, Bruce Wayne and Batman, and Peter Parker and Spider-Man, but in today's modern superhero landscape all that has fallen by the wayside. The MCU has effectively done away with the concept of the 'secret identity'. So, now that that core idea is being phased out... what does that mean for the genre as a whole? Will it survive another hundred years without this element? Only time will tell.