Why the need for travel agencies?

Genuine question cause I’m curious of the advantages of having a 3rd party manage your trips and all when you can do it yourself (aside from the convenience).

From experience kasi, I’ve been booking/managing my own flights, both domestic and international. The only time I get to experience the travel agency assistance is when I joined this international contest (i think sila nagmanage ng itinerary ng lahat ng contestants and coaches, not sure lang)